Cutting up a song into 3-4 seconds intro and exit bits.

Find the approximate location on the timeline where you'd like to split the clip, right-click and select "Split Clip" from the context menu. You need not be precise; I like to leave a little more of the clip attached than I think I'll need. Now drag the new clips into a new track while holding down the CTL key, which leaves the original in place and duplicates the cut clips. Finally, use a slip edit to adjust the exact length of the clip. It should have a fade at the front and at the end, even if it's a very short fade, to prevent clicks. Slip edits are nondestructive, so if you find you need to make the clips or their fades shorter or longer, you can do that easily.