Gesso is basically acrylic medium mixed with chalk - in this case, white.
This one gives medium coverage which I find the most useful to have in my kit. One coat is semi transparent, allowing the underneath to show through a little, two or more coats and you've got a wipe-out!
I use it to knock back imagery I'm not keen on, or that is too loud in my sketchbooks and on fabric. I also do this in found books that I want to use as a base for altering, and found papers/fabrics
Also a great base for paint on canvas and can be mixed with any of the paints to add colour
Try mixing with gelatos for some lovely pastel colours