How to start and monitor a workout on Apple Watch
One of the highlight features of the new Apple Watch is its fitness tracking abilities, which lets users track movement throughout the day, keep tabs on wellness goals and monitor specific workout routines.

To start a new workout session on Apple Watch, navigate to the Workout app.

Upon opening the app, users will be presented with a list of workouts from an Outdoor Walk to Rowing. There is also an other option if your workout does not fit into these categories. Tap the workout that best fits your routine.

Next you will choose a goal for your workout. Options are a calorie goal, time, distance, or OPEN with no goal specified. Once the goal is set, tap the Start button.
A short countdown will display on the Watch and the workout will begin.

During a workout, users can track calories burned, distance traveled, elapsed time, and take a heart rate measurement.
To end a workout, Force Touch by firmly pressing the screen.

A summary of your workout will be displayed with a percentage of completion and other stats.

Scroll to the bottom of this screen and choose to either Save or Discard the workout session.

Saved workouts and trends can be seen in the Activity app on your iPhone, while fitness data is automatically stored in the Health app.

To start a new workout session on Apple Watch, navigate to the Workout app.

Upon opening the app, users will be presented with a list of workouts from an Outdoor Walk to Rowing. There is also an other option if your workout does not fit into these categories. Tap the workout that best fits your routine.

Next you will choose a goal for your workout. Options are a calorie goal, time, distance, or OPEN with no goal specified. Once the goal is set, tap the Start button.
A short countdown will display on the Watch and the workout will begin.

During a workout, users can track calories burned, distance traveled, elapsed time, and take a heart rate measurement.
To end a workout, Force Touch by firmly pressing the screen.

A summary of your workout will be displayed with a percentage of completion and other stats.

Scroll to the bottom of this screen and choose to either Save or Discard the workout session.

Saved workouts and trends can be seen in the Activity app on your iPhone, while fitness data is automatically stored in the Health app.
Comments
Does it track everyday activity or do you have to go into the fitness app for it to track your walking and such. It is not clear if it does or does not.
The Watch will track every day activity. It will even add brisk activities as exercise. You only use Workout when you want to record an exercise by session, or want to exercise by goal.
In the end, all the data will be recorded to the same place, Health app on iPhone.
I am not sure I trust the numbers it puts out. I noticed that that the number of calories are about half those shown by the (fairly) high end treadmill at my gym. Then I saw what the problem was: The Watch records about half the distance as the machine does. I am fairly certain that the machine is closer to the truth. bpm numbers fluctuate wildly (from the upper 80s to the 150s and back) -- trust me, I do not have arrhythmia! The bpm also takes a while to register, much longer than the machine. That's a bit annoying when all one wants is a quick glance.
Also, it would be nice if the Workout app was coordinated with the Activity app. It's just not clear how they are coordinated (for example, I spent 45 minutes at the gym today, yet the Activity app registered only a few minutes of it).
I suppose I could handle the Watch giving me different calorie counts than the equipment at the gym--I've never known what to do with the 850 calories "burned" information from the exercise bike. I guess as long as it is consistent so I can compare workouts rationally, that would be a plus. Currently, I work out at three different gyms. I ride the same model bike at each. They are so differently callibrated that they give calories burned totals that are 40% off for equivelant workouts... I assume the Watch will cut through that...
I've used a Fitbit One for several years and the Watch since the 24th. I've been using both simultaneously over the last 10 days to get a feel for how close (or not) the Watch is to the Fitbit. Over this period they've agreed on steps to within 300 steps a day (out of 20k+ steps per day, 150k steps per week). They treat calories differently with, I'm guessing, Fitbit including your BMR (basil metabolic rate, or resting burn rate) and Apple including only calories above your BMR. So, Fitbit shows 2243 calories whereas Apple shows 702 in the Activity app (which is labeled "Active Calories" in the Health app). I also use MyNetDiary, synced to Fitbit, and it estimates BMR and subtracts that from the Fitbit data. The result is very close to Apple's number (within about 50 calories a day).
Unfortunately, Apple doesn't include floors climbed, which the Fitbit provides. I'll miss that, but not enough to continue using the Fitbit.
More concerning, though, is that my health provider syncs with Fitbit to provide monetary incentives to stay fit. They also sync with Moves and Runkeeper. The problem is that these apps don't access Heath app data, so reflect only steps recorded by the iPhone's M7 processor and not steps recorded by the Watch and synced to Activities and Health. This is problematic since there are a lot of times my phone isn't with me. Fitbit is (err, was) always with me, in the same way that Watch is now, and it provided reliable data to my provider. There's currently no good replacement for it that I've found. This is a missing piece that needs a solution (I've contacted my provider to ask that they support HealthKit, or partner with an app that does).
This sounds as though I'm implying Fitbit also uses the M7, which of course it doesn't. Just wanted to make it clear that I was referring only to Moves (which I'm certain uses the M7) and Runkeeper which I suspect does, but am not as certain about.
Does it track everyday activity or do you have to go into the fitness app for it to track your walking and such. It is not clear if it does or does not.
It will track "movement" throughout the day, but in order to have the exercise ring accurately fill up you're going to need to do a workout session like this.
Whether the Activity app logs something as exercise or activity seems a little uncertain, even when I choose a category in the Workout app. I tried carrying the iPhone while exercising to see if that helps. Jury still out, and I am still testing.
Bottom line, I like the watch and am glad I got it. I expect that these rough edges will be smoothed out with updates.
One more thing. I don't like the fact that using the Workout app "disables" Glances. I like to adjust music and podcasts while on the treadmill, and I have to go back to the watch screen first to invoke Glances to get to the audio controller. Then I have to go to the App screen to reopen Workout. Very inconvenient.
Have you been pressing the crown and contacts/ApplePay buttons at the same time (perhaps inadvertently)? That takes a Watch screen shot. Otherwise, I've no clue, and have not seen this.