Can i install a subwoofer to an amp myself?

I currently own a 2009 Subaru Legacy and was wondering if i would be able to pay someone to install a amp in my car, then just install the subwoofer myself? ( the subs are already inclosed and ready to go) i am hoping to cut installation costs. Also i am very bad with cars and stuff, but pretty good i guess with wires, i just am afraid of shorting out any circuts or screwing up, so guess not good enough to install the amp, but hopefully good enough to install the sub. thankyou so much for the help!