Re: Ithaca M-66, I want to try trap. Help
It will get you started. Trap guns are generally tight choked and not unlikely double barrel. Most shooters change the choke using screw in tubes, your Ithica likely has a fixed choke (likely full).
The 870 you mentioned is a fine type for skeet/trap if you are comfortable with a pump gun. If the 870 has screw in chokes and a regular length barrel learn to shoot it and you have a better starting point than the Ithica.
Talk to the guys at your range and bring both guns, learn a few basics, ask for help and have fun.
Should you use the Ithica there are cilp on front sight beads that are much more visible, it may help.