Take a look at the parts. Most stands have a base, one or more tubes, and a shelf. If there is a latch, knob or screw on one end of the larger tube, release or unscrew it and insert the smaller tube. If you see only one tube, release or unscrew the fastener and tilt the tube to allow the inner one to slide out. Tighten the screw or knob or adjust the smaller tube until the latch catches.
Squeeze the latch or unscrew the screw or knob on the base and insert the bottom of tube, if they are separate. Slide the tube in as far as it will go.
Open the legs until they lock in the tripod position. You may first need to squeeze a latch or unscrew a knob that is holding the legs in place. Re-tighten and set the stand on the floor.
Slip the shelf onto the upper end of the tube. Use both hands to pull down the sides of the shelf.
Adjust the height of the stand by loosening the latch, screw or knob connecting the tubes and pulling up or pushing down until you get to the desired height. Tighten the knob or pull/push the smaller tube until the latch catches. On some stands, you can adjust the angle of the shelf either by pressing right on the shelf or by loosening a knob, moving the height to the desired angle and tightening the knob.