That pipe does not appear to be a very strong one (the wall thickness of a pipe tends to increase with its diameter, so narrower pipes are usually also thinner ones).

You can mount a shelf to it, but I'd recommend ONLY storing spices, or maybe a single small plant. Don't try to add a bunch of shelving and store pots and pans and half your kitchen on it.

There's a variety of pipe clamps out there, many of which can be used to hold something against a pipe. The exact design is up to you, the tools you have, and the types of pipe clamps you have access to.

A couple of these generic pipe clamps screwed into a block of wood can act as a decent base for a small shelf, which then gets screwed/glued to the block of wood. You gotta get the sizing of everything just right, though, to get enough clamping pressure.

"Split Ring" or "Split Clamp" pipe clamps are much stronger, but will take a bit more creativity to attach to wood.