Drywall roll texture is done by rolling the drywall compound onto the surface. The roller creates a pattern in the mud. Once the pattern is semi consistent the mud is allowed to dry. Use a heavy nap roller, around 3/4".
Mix the mud so that it can be rolled. Much heavier than paint, but thinner than taping compound, approaching a liquid state. Roll the mud on and try to blend it into the surrounding area. If your texture seems too heavy or light, adjust the consistency of the mud. Or try a different nap on the roller.
Don't despair, drywall roll texture is a pretty messy operation. Make sure you cover everything you don't want drywall mud on. You will still have some clean up to do.
This is by far the easiest texture to deal with. Step back and give it an inspection. Not satisfied? Scrape it off and try again. Looks good? Great, your drywall texturing experience has been successful. Time for another exciting activity, like cleaning the basement.