How do I use this stamp set?

The 3 big stamps look like they slot together, but I have no idea what shape that's supposed to be.

I have this too and came across it in my stash the other day! I said "huh?" and put it back away so I wouldn't have to think about it.

Looks to me like a hexagon theme. The striped, script, and diamond shapes can fit together to make a big hexagon. The other shapes can be stamped multiple times to make a hexagon: the shape above the striped piece is half a hexagon, three diamonds can fit into a hex shape, as can six triangles.

Looks to me like it's supposed to be some 'random' backgroundstamp, possibly for smaller projects like planners or PL-cards. Because the shapes themselves don't make much sense.
Does that black half-hexagon fit into the hexagon-outlined-stamp?

I would use the striped stamp as a background in my planner, stamped in a lighter colour, and then write an appointment or event on top of it. Or a sticker on top.

I may be shape-challenged, because I don't see any known shapes in there, except for the diamond and hexagon.

I'm no help with your question, but had to add I think this is the dumbest stamp set ever. It ended up in my donate pile.

I went to go search the gallery over there and you can't see DT contributions earlier than the current month's kit...I looked at it recently and that wasn't the case then...wtf?

I swore it was working just last month.  That's crazy.

I asked but, honestly, didn't get much wiser. You are supposed to combine the shapes in some way. Haven't used this stamp set yet.

The weird shape on the bottom is half a hexagon. Turn it upside down to stamp a full hexagon. Or, you can combine the obvious half hexagon with the small diamond and the weird shape to create the larger hexagon. As far as the other shapes, they remind me of quilting, where you can combine to create patterns. Something like this: