To leave a space, you do not need to log out. You can simply close the tab or web browser to leave the space when you are done for the day. The moment the tab is closed, Gather will no longer be transmitting audio or video from your device to others in the Space.
If you have logged into an account and would like to sign-out in order to log into a different account, you can head to https://gather.town/app and find your name on the bottom right. Click on your name, and the below image should pop up where you can click the Sign Out button.
You can also sign out by directly pressing on your bottom menu inside your Gather space and clicking the 'Sign Out' button.