I'll go through both systems
Your deltoid protectors are easy, put your arm through the strap, and the velcro on top of the strap velcros to the inside of the OTV. There's also a velcro strap on the outside of the armor part and runs vertically, its about 3" long or so, that bit attaches to the strap that keeps the front and back section of the OTV together. It'll prevent the deltoid protector from moving side to side, as well as keep it tight to the armor when your putting it on or taking it off.
now the arm protectors
The big straps at the top of the protector go OVER your shoulder padding on the OTV, down into the neck hole, and then bring them back out through the arm hole. So it velcros both on the inside of the plate carrier where the deltoid protectors velcro'd in, and velcros back onto itself.
Now put the plate carrier on. The arm protectors should be flopping over your arms, you want to secure those down. So unhook the velcro from the base of the protector, and it wraps around your arm, and velcros back onto itself.
coincidentally, if you search "OTV DAPS" on google, the second picture is of me from the back modelling my OTV with the DAPS system on it and wearing OD pants