Welcome to the forum!
I can't think of any tutorials. There's always the manual, except it might not be entirely up to date (Help menu > Inkscape manual).
But here's some info. You can change the space between all the characters, using this spinbox
. Or if you highlight just part of the text, it will change the space between only the highlighted characters.
Or if you want to change it between just 2 characters, or if you want different amount of space between different characters, place the cursor between 2 characters, and change the value in this spinbox