Set up:
Many of our folding tables have locks to help keep them in position easier. If the tabletop folds in half, there is usually a catch on the end opposite of the hinge.
While the latch is simply released in the first image, the second has a wider opening near the middle that is used for a fingerhold. To open, simply pry the two ends apart. This will release a catch on the underside of the tabletop, similar to the one pictured below.
This catch encircles the crossbar for the leg. It can take some oomph to separate but will neatly keep the table folded when not in use.
Folding for Storage:
If the tabletop folds in half, look for a latch near the center of the table similar to the image below. There will be a matching hinge without a lock on the opposite side.
To fold, press the lever and fold the tabletop. The latch locks automatically when the tabletop is fully unfolded.