Tap washer? That could mean various different things. Older faucets and hose bibs actually had replaceable washers which were held in place with one screw that usually broke before it came out. So I'd have to replace the whole thing. But you'd have to unscrew a big nut first to get the mechanism apart: a big adjustable wrench might work for that, or vice grips with a rag around the nut, or even a pipe wrench - same rag.
All these threaded parts are going to be totally gummed up with hard water deposits that will need to be dissolved with some kind of penetrating "oil", like PB Blaster, or even WD-40. Put a bunch on and let it sit for 1/2 hour. It sometimes helps to tap on the nut with two hammers simultaneously on both sides. Work your way around if there's room.
Once that's off you can unscrew the washer holder out to get at the washer. Do you have washers?
Again, unless you've got all the proper tools, washers, replacement washer holding screws, etc. it's easiest and cheapest to replace the entire faucet. But getting it out might require other tools like a basin wrench or even soldering equipment.
Just be sure you can turn the whole thing off when you have to go to the store or get some help.