OK, to select tracks, you have three choices (that I know of).
1. Use the tracks table in either the edit or mix windows, and find the track(s) you want, and press VoiceOver Space on them.
2. Use control p to select the previous track, and control ; to select the next track. Either of these in addition to the shift key will select continuously.
3. Use a control service with select (sometimes called del buttons).
When you’ve selected the track(s) you want to manipulate, you can check your selection by pressing shift s (solo). This will solo the tracks which are selected, so you can ensure you got the right tracks.
Now as I said before, you can use the down and up arrows to select pieces of audio as you play - for this this, I believe you have to have “Link timeline and edit selection” selected in the options menu (shift /).
Alternatively, as Chris said, you can just figure out which portion of the song you want to select, and type in the numbers.
A final one, and one I really like if the numbers get too confusing, place a marker at the start, then set your play head to where you want to end, then you can just hold down the shift key while typing in the marker location. So, for example, if the marker is marker one, you can find the other part of the selection (this works backwards or forwards), and hold down shift, and press numpad ., numpad 1, numpad .
HTH, and sorry it’s so long winded, but I wanted to get everything I could thinkf of out there! :-)
Cheers, and good luck!