Very new to this app & recording. How can I trim the beginning from all tracks at the same time?

Welcome CharlesStout
I think the easiest way to do this, while keeping all tracks in sync, is to use the 'Slice' from the hotbox. A little known feature of multitrack is that if you do the Slice when "close" to the Playhead, the slice will be done at exactly the playhead location. So to use this technique:
1) Move the playhead to exactly where you want the song to start.
2) Use 'Slice' on all the regions by selecting each region and opening the Hotbox 'close' to the playhead (by close, within the playhead handle bounds).
3) 'Erase' the regions on the left side by selecting them and then Hotbox -> Erase.
4) Select all the remaining regions all at once, and move them all the way left (Hotbox -> Move)

It's important that you select all the regions at once when moving them, so they stay in sync. To do this, tap each of them one at a time, then open the Hotbox directly over one of these selected regions and 'Move'