You can track your weight and several body measurements under the "Track Body" tab of your account. The weight tracker is on the main page of that tab, and you can locate all the other body measurements by selecting the "Weight" drop-down icon.
To get started, enter your weight for today under the "Enter new Weight Log" section. You can also set a goal weight to track your progress. You won’t see a chart of progress until you have two entries but you will see the entries listed below. Each time you make an entry, it’s stored and graphed for you, for each body metric.