You can do one of two things.
Follow Tygo's advice and dry hop in the keg, or just dry hop in primary. There really is no reason to transfer to secondary, unless you plan to do a secondary fermentation (fruit or such).
If you dry hop in the keg, use a small sack or tea ball and suspend them in the keg (most people use unflavored dental floss).
If you dry hop in primary, you can just toss them in, and by day 6 or so, they will be down at the bottom with the trub, and you can just rack to the keg.
The beer is always conditioning. If it is done, it can go right into the keg. If it isn't done, wait to dry hop until it is.
dry hopping makes the beer cloudy. That's what it does.
I usually like to dry hop for 7 days, because it is easy. anywhere from 4-7 days should be fine.