You can add your activity manualy but you can only add specific workouts or exercises.
If you are commited with a healthy lifestyle and want to start tracking the exercise you do regulary we suggest you start with a simple and free app, such as Apple Health for iPhone or Google Fit for Android. These apps track all your daily activities without even having to open them before starting a new run or walk. You'll find links on their respective pages. Once you've downloaded the app and signed up, come back immediately to connect and synchronize everything! :)