It is a TON to digest at once. Honestly, I would not worry about making calls until you feel 100% comfortable about skating while keeping your eyes on the action continuously without crashing into anyone else. Once you've mastered that, now you can start to judge the action.

When you begin to judge the action, don't bother calling or verbalizing anything externally. Watch, think in your head "Was it a major? Whistle, Color, Number, Penalty, Major. Was it a minor? Color, Number, Penalty". Get used to having that mental framework so you're used to thinking of the skaters as Color+Number, and the penalty as the abbreviation and hand signal.

Once you get pretty comfortable just with the mental framework, you can start to make the hand signals, and asking skaters during practice for feedback: "That looked like she back blocked you, where did she actually hit you? It looked like that wall was using their arms to hold you back, was that actually the case?" On more complicated penalties, confer with other refs: "I saw this complex situation. Who should have gotten the penalty?"

Once you feel pretty confident you're seeing the initiation, the penalty, and the outcome correctly, start to verbally call, whistle, and signal as appropriate. Do this during practice, as you're going to make a LOT of bad calls. You're going to stumble over trying to retrieve an offending skaters number from her arm while they're jumbled in a pack. You're going to call things that were minors as majors. You're going to lose track of the action due to collisions with skaters in the ref lanes. It's going to be very, very difficult :)

tl;dr: To avoid being psyched out, start slowly and have very low expectations for yourself. Master skating, watching the action, avoiding fallen skaters and other refs. Memorize how to call penalties. Call them in your head until it comes out right every time. Get feedback from the skaters and other refs. Once you feel comfortable with the notion, verbalize. Screw up. A LOT. Keep at it, because practice makes slightly better than before.