DO NOT try to take masking off damp paper. A rubber cement pick-up or soft eraser will lift masking off your paper. Remove all masking fluid from your paper as soon as possible. Don't leave it on the paper for an extended period. You paint masking fluid on with a brush just like paint.
Most artists use masking on small areas within a painting so a small brush is needed.
It is very difficult to get out of your brush so never use good brushes. Shake your bottle of masking good before using. Get a small container and add a drop of dish soap and some water. Dip your brush in the soapy mixture then blot dry, THEN dip the brush into your masking fluid and apply to your painting. Rinse with clean water and dry after the soap bath.