Hello! Please see the pictures for any clarification...

I have a 2 switch box in the bathroom: 1st switch controls the vanity lights-- 2nd controls the exhaust fan.

Wanted to put a dimmer on the vanity lights, so replaced the light switch with a dimmer.

Now, the vanity lights dim, but the exhaust fan switch does not work! :^O

What to do?

Check your wiring. You obviously discontinued the feed to the fan switch.

With a tester find out what is the line side and what are the switch legs.

Thanks for your answer stanforty! I will humble myself and say that I need to hear it like I'm brand new. I've changed dimmers in the whole house, and it was just by "look and replace". I don't know what a "line side" is or what "switch legs" are. ;^)

Because this is electricity I want to make sure it gets done right...

I do have a tester... a digital one. I'd have to do it with the electricity on? Dumb question I know, but I want to live.

Here are some more pictures that I didn't post before. Thanks!

In you pic ,I'm sure you know, the switch isn't connected to anything. Connect the black wire with the separated insulation to one terminal and the other unconnected black wire (which looks like is hiding behind the switch) to the other terminal

What HK said.
It looks like that "loop" with the insulation stripped from the middle came off the switch. I bet the other wire is just stuck in the back of the switch.

Had a long post but just deleted it. Read hk and stan's replies over and over, and then something stan said hit me.

The wires are still hot, so I touched the stripped insulation to the second screw on the toggle that's still installed (see second to last pic)

A spark and the exhaust fan started... a big fat duh for me. Didn't totally rehook up the new switch.

Thanks! The insight pointed me to the obvious... (slapping forehead)