best shortcuts for beginners: how can I toggle between bass and treble clef????

Since there are many clefs, you can't toggle between them. You can , however, drag a clef from the clef palette or use the preset shortcuts [Ctrl]-y, [Ctrl]-1 and [Ctrl]-y, [Ctrl]-2 to place, respectively, a Treble or Bass Clef.

Look under Edit >Preferences >Shortcuts for other preset shortcuts and to modify existing ones or to set your own.

I'm kind of assuming you don't really mean that you want to change clefs on the same staff, but rather, that you wish to move the note input cursor from one staff to to another (there could potentially be lots of staves, but I guess you are thinking of piano music that has exactly two). The default shortcut to move the cursor up and down is Alt+Up/Down, I believe, I customized mine because my computer uses that combination for something else. See Edit / Preferences / Shortcuts for the full list of cmmands and their shortcuts. There are commands that move through notes within a chord then through voices then through staves, others that only moves through voices and staves, others that only move through staves.