You want the peppercorns (white and black) to be cracked and chunky, not a powder. My blender will go in reverse, so I just use that, smacking the corns with the dull side of the blade. A blender or food processor will work, just be careful not to reduce too finely, and avoid the dust/fumes.

The "Pink Salt" is the curing salt used for corned beef and pastrami, etc. It is not Himalayan salt.

The coriander is just crushed, not reduced to a powder. Again, I use my blender in reverse. Any other method will work.

The garlic is the coarse granulated type. It may be harder to find, but it's size seems to be important. The granules are about the size of the head of a pin. The size helps keep them distributed in the rub instead of settling down tot the bottom.

The Onion is the dried onion flakes, just broken up a bit to be about the size of the garlic. You don't want powder, but I think the normal size is a little big.

I use the red pepper flakes like you put on pizza or an Italian sandwich. However, I give them a whirl or two in the blender to break them up a bit.

FINALLY, just mix everything together with a whisk. Be careful about inhaling the powder/dust. That can be very unpleasant.