Purchase a Domain Name & Hosting
You can do your research and study which ones are the cheapest, offer the best services, etc. I can also show you where I go. The links below are from Bluehost are ads. Please feel free to utilize them or research your own source for a domain name and hosting. Bluehost has both Hosting and Domain names in one place and I've been using them for years. As of the time of writing this 11/28/2018 Bluehost offers free domains with the hosting options I recommend.
Choosing a name for your locksmith website isn't as hard as one would think. You want to first decide if you will use a keyword based domain or a domain based on your business name. Ideally, both would be the same. It may be better if your business is named Toronto Lock And Keys (if you live in Toronto) than it would if you named it Name Company. That being said, doesn't mean you can't have a successful business either way. There are many large companies with names that have very little or nothing to do with what they do, They do well without utilizing this tactic. Pick what you like. I do recommend it be short as possible (while still being easily remembered).