It’s a multiple clipboard manager app.
The Mac’s clipboard is what stores whatever you copy or cut within a document or an app. OS X simply copies over whatever was last copied. A multiple clipboard manager remembers what was copied and gives you the option to paste it again without copying first.
There are plenty of decent multiple clipboard apps, but if you’ve never used one try CopyClip first because it’s decent and free.
Whatever you copy gets saved in CopyClip and becomes accessible in the Menubar from a list of recently copied items.
There’s not much to setting up CopyClip, either.
Set the number of clips to remember, and the number to display in the drop down Menubar. That’s about it. CopyClip is free and easy to use but not necessarily the best of the multiple clipboard manager apps as it requires an extra step to paste an item into a document. There’s also PTHPasteboard and CopyPaste Pro, both top notch but each with a price tag.