The timeline should be at the bottom of the editor window, if you're in the default design workspace. If you started in the mesh editor workspace then "design history" might be turned off, in which case you wouldn't have a timeline. It looks like this:

https://help.autodesk.com/cloudhelp/ENU/Fusion-Assemble/images/animation/timeline-groups.gif

If some of the icons are highlighted in yellow, those have errors, so, things like broken projection links, or missing objects for some operations. You can usually fix those and patch things up.