I'm new to this!! The check engine light is on and code 21 and 12 are coming up. It starts hard after it sits for a while but once its running its okay.

I'm assuming you have a first gen legacy 90-94 with MT. I would probably ignore code 12.

 

The hard starting symptoms are analogous to a bad temp sensor, which is code 21.

 

They can be had for about 20 bucks or so at www.1stsubaru.com

 

I'd start with that and see how things work.