Yep - as above, brush on the resin and then sprinkle on sand/gravel...the resin is sticky enough to work with like that for about 4-5 mins so i just did a bit of resin....bit of sprinkle
It was the most fun part of the build!
Give it 2 hrs to dry hard then hose it down to remove the excess (there's LOADS...i did the sprinkling in a large tub so i could catch the excess i applied) After the hose down...leave one day to dry then touch up with more sand in any spots missed on the first run. Wait 2hrs......done - stick in the tank (or do like me and wait for months because you are too busy to fill the thing!)