Result: 6× Smooth Sandstone Slab
Smooth Sandstone Slab is a shaped crafting recipe that uses 3 items: 3 Smooth Sandstone. Place the ingredients exactly in the pattern shown above. The pattern can sit anywhere on the grid as long as its shape stays the same. It needs the full 3×3 grid, so you have to use a crafting table.
Read the Smooth Sandstone Slab article in our Minecraft wiki
You need 3 Smooth Sandstone — 3 items in total, arranged as shown in the crafting grid. The recipe gives you 6× Smooth Sandstone Slab.
Yes. The recipe needs the full 3×3 grid, which only a crafting table offers.
It is a shaped recipe: the arrangement matters. You can shift the pattern around the grid, but the shape must stay the same.