Hello,
I’m sorry if this issue has already come up, but there are too many pages to read.
I’ve been trying all afternoon to cut the beginning and the end of a recording, but haven’t been able to. I’ve read all the tutorials available…
Could somebody please help me?
I’m using Audacity 2.3.2 and am on Mac Mojave.
Many thanks in advance. 
Select the portion you want to remove, then click on “delete” in the edit menu.
You’ll have to do this twice: once to trim the start, and again to trim the end.
(You can do both at the same time by selecting the section you want to keep and pressing “Ctrl”+“T” keys).
Thank you Trebor for your reply. What I hadn’t understood is that I had to select the portion to delete clicking within the tracks where the “hand” feature appears (and not from the top with the green arrow). It was soooo utterly frustrating. Done it now. 
Something I just learned as another new learner, is that you can also clip the file in various spots. If you use the selector tool (the one that looks like a capital I), click the waveform somewhere, then hit ctrl+I it’ll split the track into two different clips. Then you can rearrange them if you need to, or delete small sections that have been clipped up, or whatever you need later down the line. It can also be done by selecting where you want the clip again, then choosing Edit → Clip Boundaries - > Split.
Then, if you want to rejoin the files into one clip again, you can use the time shift tool (looks like <->) and just click the clipped line and the clips will merge together again.
That is not strictly correct. You don’t have to select the Time Shift tool in order to join clips by clicking on the clip line between them. It works with any tool except the magnifier tool.
Please see this page in the manual for a full explanation of how clips work.
See also this page on selecting audio.
– Bill