Molecules have slight positive and negatively charged areas on them. Single bonds can rotate more or less freely assuming the parts they are attached to aren’t too big and hit each other. So it’s almost like they are slightly flexible magnetic rotatable chunky things, and the way they fit into a receptor, (also a chunky magnetic flexible thjng) is by their positive and negative areas matching up with negative and positive areas of the receptor.

It sounds like it would take forever, like it must take so much vibrating around for the exact molecule among millions to slot into place, but molecule speeds are insane, they move FAST. There are enzymes that can grab a molecule, break it apart, let the pieces go, and repeat with s new one…60,000 times in a second.

Lol I tried to make a quick answer ha