I'm just starting F/A 18 OCU.

First lesson includes a barrel roll. Here's a clear video explaining the process and movement.

https://www.youtube.com/watch?v=R9LxOjPnoe4

I struggled with the barell roll, felt counter intuitive pulling down inverted so i kept doing the 1st part fine and then just rolling out at the top

An excellent piece of advice John. It's a nice video but not a safe technique, unless you are very high.

At FTS, we always drummed into a student that if your wings weren't horizontal before your nose was passing through the horizon, when inverted, - roll out. You also need to vary the aileron input according to speed to keep a constant roll rate.

Of course, for a lag barrel roll against an opponent, just put him in your right (or left) hand side of the windscreen and roll around him.