Andre, if you just come from Garageband I guess you should take your time to go into Logic from the ground. It's a complex and very rich software wich can't be improvised, especially if you want to write for orchestra.
The tutorials I've studied untill now and that I've found generally very usefull are:
1. Logic Pro 8 101 (M.Sitter,) to know the software in general.
2. Logic 201: Master class (S. Horelick)
3. Logic 303 TNT & TNT2.
and, of course, the manual.
You will find a lot of precious informations, but none is speciallized on writing in the score, because Logic is not a software especially dedicated to this (as Finale), but you can anyway do it at a professional level.
It will take some time, but it's worthy.
good work to you