If it's a manual awning, there should be a black fabric "tab" hanging in the center of it when rolled up. You need an awning rod to stick into the loop to pull it open. Most likely, there is a release lever on the forward end of the roller than you need to pull with the rod first to unlock it in order to open it. To roll it back up, hook the rod into the strap and THEN activate the release lever. It is possible if it's manual, that the previous owner (or operator of the awning) let it retract without using the rod and the strap got rolled into the awning. You may need to use a ladder to start unrolling it, if that's the case.
Normally, a manual awning has arms that run all the way to the bottom of the trailer. They will also have large handles about midway that you use to adjust the angle once it's extended. The "arms" can actually be detached from the trailer wall and used as legs, to get them out of the way under the awning ends.
For an electric awning, there should be a switch inside the rig, near the rest of the switches. Electric awnings typically do not have mountings that extend to the bottom of the wall and don't have handles on the arms to adjust them. There is no manual method to extend an electric awning and retracting one "manually" if the motor quits needs to be done very carefully.
