The most basic way would be to select a block of frames, right-click and choose Copy Frames from the context menu, then select blank frames at the end of your spans right-click and choose Paste Frames.
You can also do this via the menu or shortcuts: Ctrl+Alt+C / Ctrl+Alt+V.
Another option would be to select a block of frames and drag it to a new location while holding down the Alt key.
Yet another option would be to learn about Graphic Symbols and nest your animation in looping containers.
Generally speaking, you need to get familiar with the features of this program so that you can actually start using it.