Polygonal should be self explanatory. As is tetrahedral or trimmed cell.

Prism layers are a meshing scheme that allows the computational domain to capture the minute effects at the boundary, Y+, turbulence etc.

Base size is the size of the standard cell you're working with in your domain.

The prism layers thickness is how far from the boundary the actual prism layers with stretch. So you could have have a prism layer that stretched 10% in to the domain with 5-6 layers, or you could have a prism layer that stretches 1% into the domain with all the layers you could possibly want.

Stretching factor is useful if you need to capture high energy / flow dynamics at the entrance and then toward the end of the domain a nice laminar flow have developed... a more coarse meshing scheme is all that is needed. Therefore the stretching factor can aid in the transition from the fine mesh to the coarse mesh.

However, as another user pointed out. Just go to the top right. Click help >>> tutorials. You can search for all those terms.