Plumbing 101

Part 1 Repairing hosebib

out of the ground with a cap on it. The cap is missing a chunk of it but it still screws on but when it rains water and stuff can get in it. What is this thing, and does it matter that it’s broken, and if so, where do I get a new cap for it and what is the cap called? Thanks.

I’m trying to save money by replacing the outside faucet myself. Is this something I can do myself, or do I need a professional plumber to do the job for me?

Please help. Thanks