Have you ever done paper mache? It’s very similar, except your using glass cloth instead of paper and epoxy instead of elmers glue.
The way I did the first layup, I set the dry cloth (use chopped mat, not woven cloth for the first try) in place and cut it more or less to shape, with 1" min extra all around. check to see if I have everything ready, take a deep breath, maybe a beer, then I mix. Right as I mix the stuff, I start a timer. If it says 20 min working time, you have 20 min, including mix time.
The mixing is important. A crappy finish and weak parts are often due to insufficient mixing. has to be well mixed without mixing too much air into the resin and making foam.
Once your mixed, I pour some out in the middle and gently push the blob around to the edges, working the cloth around the shape as you go. It takes a couple minutes for the resin to soak the cloth, let it flow, try not to push the resin into the fibers too much. squeegee (or brush) off the extra, but not too much squeegee. Alternatively, you can wet the resin first then lay it out, but that works best for small (pre-cut) tabs, like for reinforcing corners and joints. It hardens slowly, so you can mess with it a little after it starts to “kick” but not too much. let it harden overnight, then use a razor to clean up the edges, maybe knock some high spots off with a surform. let it curr completely before sanding. (cut soft, sand hard).
if you did good work, you will have little sanding, if not you will have a lot of sanding to do. Sometimes if I have a lot of low spots I fill then sand again.
the gloss coat is a layer of resin over the (now hard) shape to bury the cloth texture. this is poured then lightly brushed so that it completely coveres thee part and drips a bit on the edges. a good gloss coat may not have to be sanded.
You can continue to add layers of cloth and/or resin to get the shape you want.
remeber, there are no mistakes, only more sanding 