How to mount studs?

I have a hottub I just removed and I want to use that 8x8 slab as my patio and build a u-shaped island around it. My question is how to I secure or mount the studs to the area outside of that slab which is just grass.

Do I have to pour footers or could I use 8x16 concrete slabs as a base and put the wood frame on top of that?

Here is the area and an example of what I’m after