The series of videos above are great. The guy who demonstrates above spreads resin entirely with a foam roller.
I often pour it out in a long puddle and then stroke it out smooth and flat, from end to end on a long panel, with a 12" inch drywall trowel (mud mongers call it a knife). For wetting out a large area, perhaps a 4' foot by 16' foot panel, a foam roller takes waaaaaaaaaay way too long.
Pour the resin out in a back and forth side to side line. Then spread it with a wide trowel. Keep the trowel in a bucket of acetone or denatured alcohol. I keep a stiff brush in the acetone bucket too, so I can scrub all the various sized and shaped trowels I keep in there, each time I return them to the bucket.
Use glovez and know that acetone is flammable.