What is meant by inside shoulder is your leading shoulder when you're spinning. so left spin inside shoulder would be left. right would be right
If you're planning on spinning left, its easiest to appraoch the right side wall. Its basically the same thing as doing a cork 5 on a jump. Pop and drop your left shoulder slightly so you're looking more towards the ground at the beginning of the spin. Do not set the spin like you would a regular spin, cork 3's and 5's are set more so with your hips and legs than throwing your arms into it. Push out with your hips and keep your eyes committed to the spin and where you want to go. You should be able to see your landing zone pretty easily through the entire trick unless you're airing far down the pipe. The trick should come around pretty easily as long as you stay relaxed and stay on the right axis (cork). Learn how to do a basic cork 5 by itself or with a safety before you try grabbing tail on it.
The one thing to emphasize most is that cork 3's and 5's aren't thrown the same as 7's, 9's, etc. Learn how to 'throw' the trick more with your hips and legs than your upper body. The only thing you really need with upper body is to drop your shoulder slightly at the beginning.