Lark tracks your activity by reading data from your phone's sensors. When you move around with your phone on you, your phone detects that movement and determines what kind of activity it is (walking, running, etc). Lark then reads that info from your tracker and interprets it accordingly.
When exercising, we recommend bringing along your device with your Lark app installed so that your activity is automatically logged within Lark.
If you forget your device, you can always add your activity in manually, by:
First, tapping the "rainbow bars" icon in the top left corner of the main chat screen, and then selecting the activity icon.
Finally, select the plus icon in the lower right hand corner of the application.