In some cases you have too many timelines to scroll through, and you just want an easy way to find the one you need. On web you can go through collections, the "Created by me" or the "Shared by me" folders.
Searching for timelines on mobile is easily done by entering the tab at the bottom named "Search". Here you can select between searching for timelines, items and activities. Select "Timelines" and start searching for the timeline you are looking for.
If you wish to filter timelines you can press the button on the top right corner to filter between tags and sharing options, in addition to free-text search.
Favorites are at the moment only available locally on the phone you are using. That means that the timelines you favorite will be stored locally on your phone and will not show when you switch devices or use Clarify in the web browser.
To favorite a timeline, enter the timeline and on the top press the heart button.
Find your favorite timelines in "My library" and enter the "Favorite" section. Here all your favorite timelines will be listed.