I will try to make time to attach some pictures later, but basically, if you're designing something with multiple parts (components), when you hover your cursor over your component in the part tree on the left, a little gray dot will appear. If you click that, it will isolate that component from the rest of the assembly.
What that does at the same time, is isolate all the actions you've made in the process of building that part/component in the timeline at the bottom. So rather than having to sift through a huge timeline, you only see the timeline items related to the building of that part (component)