If you're locked out of your house first think does anyone else have a key who I can get a hold of. Secondly, if you are renting contact your real estate agent and see if they can come and let you in. If you have exhausted your options, you can call locksmith. For a fee they will be able to get you back into your house.
A locksmith can rekey your house and make all locks take the one key. This makes life easier as you only need one key rather than carrying a bunch of keys with you.
Yes, a locksmith can duplicate your keys for you. Simply take your key to be duplicated to a locksmith and they'll be able to create you a copy.
Usually these are done on the spot. If the key type is not common and blank needs to be ordered in then there can be a wait.
Yes, car keys can be cut by a locksmith. A modern car key also needs programming as these often contain chips in them nowadays. Having a locksmith cut a car key can be much cheaper than getting a car key from the car manufacturer.
Yes, many locksmiths offer 24-hour callout. Ring around to see who is open when you get stuck!