You'll notice the red plastic handle has a notch in it. Straighten the arm out and then push the window open far enough for the notch to set down on the frame and it will keep the window open for ventilation. Ours was really stiff at first but after using it a few times it loosened up a bit and now opens easily.
TT: 2015 Jay Flight SLX 195RB Baja Edition
TV: 2014 RAM 1500 Big Horn CC, 5.7L Hemi, 8-spd, 3.21LSD, Factory Air Ride/Tow Pkg, Andersen WD/SC