Many ways to do so. Easiest would be to make a black bitmap in your photo editor, then choose to Ripple all tracks (from the track hamburger menu) when you drag it in from the playlist. Any excess green space you can right-click ‘Remove’.
Probably best to do your research before posting then multiple editing your post
If you want your text to fade-in/fade-out during a video clip - split it and copy the section to a new track and apply text and fade to that. (Make sure V1 has composite mode enabled and that the fades have the check box marked to adjust opacity)
A far easier way to add a black segment is simply
File>Open Other>Color.
This will create a clip of the color you choose (default is black). Default length is several minutes. Trim this to the desired length (use in-out points).
To add text:
Filters>Text
Type desired text in box. You can choose color, font and size.
Add to playlist, position playhead at insertion point, then insert into timeline at playhead.
Click on black clip in Playlist
Set Playhead at desired insertion point
[v] will insert clip/image at desired point (i.e. at Playhead)
Items to the right are pushed to the right. Timeline is made longer.
So you see there is no need to leave the program or the project to accomplish this.
As for FAQs, no program paid or free ever has a long enough list. My own solution is to create my own “tips & tricks” document (I use Word), find answers to my question on forums like this, then save them in my list. For every digital anything I’ve ever used (including cameras) this has been necessary to have a ready reference and reminder…