I just realized you asked about the process! Sorry!
So that stuff is just a patch kit, you don't need to worry about the advanced stuff like gelcoats, vacuum bags, ect.
Start by taping over all your seams with masking tape. Put your tape on the "show" side that you want to be nice. The resin will leak thru any gaps, so make sure you get complete coverage. Also 1 continuous, straight piece of tape is better than multiple pieces, but multiple pieces work better than trying to curve the tape to the side. If you have an indent like -_- you can fill in with kneadable eraser, or use a dremel to get the resin out after it's cured.
Then you need to decide how you are going to layout your FG mat. With my helmet I started with about 1"strips over the seams as my first layer, kinda like you did with the masking tape on the other side, then a second full coverage layer. Note, this isn't the "proper" way to do this, but it's going to be walking around a convention, not Mars (not yet
). The important part is, decide your layout, draw your pattern up on your mat and cut out all your pieces before you go on to the next step.
Next mix your resin in a disposable cup. it's only a few drops of activator per ounce of resin. It's not exact, the more you put in the less work time you have, but the cure is faster, and the less you put in is pretty much the opposite on both counts. Either way you will still have a long work time, and the cure is going to be 1-2 days.
Get your brush and start applying resin to where you will being putting your first piece of mat. You don't need to go heavy on the first coat of resin, you're aiming to get the mat to stick at this point. After you get all your pieces laid up, take your brush and DAB the mat with more resin, because if you stroke your brush you are likely to shift the mat. This coat you can go thicker on, you are looking to completely saturate your mat, no dry spots, and try to get any bubbles you see behind the mat squeezed out.
And that's it! put it somewhere it can cure, or do a second layer. I would recommend a second layer personally, especially if you did like me and only did the seams on the first layer, but again, we're cosplayers not actual space marines.
Hope this helps!