all struming is in a up down pattern or (down up) whatever. The trick is to know the speed of the strum or when and if it changes and more importently which stroke being up or down to miss. ie up (down miss) up, down gives one sound followed by a pause then two sounds or chords followed one after another. Sorry that may not help ...
If your starting out then just do slow down strokes to a song beat, as you go do down and up, and see what goes...you will understand eventually. Just remember, playing chords is essentially knowing when not to hit the stroke on the down or up.