Easy elbow joint?

Hi, I'm making an indoor trellis that's changeable- repositionable. So
it involves an elbow joint between two 1" by 2" by 4' boards of wood.
I'm a total beginner and don't know what I'm doing.

So, I want the two boards of wood to be connected but able to rotate,
the way your forearm rotates around your upper arm. I also want to be
able to "fix" the joint in place, so that it's immovable, but then
easily loosen (unfix) it to rotate it into a new position. Am I
explaining this terribly?

Maybe this will help- My original plan was going to be this- Where the
two boards of wood meet, I was going to just put one nail to connect
them. That way, I could rotate the "forearm" of the elbow around.
Hence, an elbow joint.

And then I thought that would be too loose, so I though I'd put two
nails in, and when I wanted to reposition the forearm, I would take
one nail out, and then move it into a new pose, and then put the nail
back in.

But then I thought this is probably a common problem and there's
something I can buy at home depot that does this? An elbow joint
that can be "locked" and "unlocked"?

thanks.