The above advice is absolutely the best advice and you should follow it.
You would be wise to avoid reading the following. It is well off the beaten track.
Personally, I prefer to practice active cellarmanship. That is, I never have a gas line attached to any keg unless I'm actively adjusting its CO2. I only apply CO2 to each of my kegs individually throughout their time on tap. It's a busy, inconvenient way to dispense, but I much prefer the intimate involvement it provides with the beer you brewed. Initially, it's a pain, but once you get a feel for it, it's really easy and it allows you to manipulate the beer, learn about the beer, and put the beer in its best light.
More importantly, it allows you to serve several beers with different carbonation demands from the same fridge and display them in their best light. You can't seriously say that the same fridge can do equal service to a UK bitter, a German lager, a US IPA, and a German hefe. Cellarmanship allows you to do that. Unfortunately, it can't help with the various ideal temperature needs of those beers...but it can get the carbonation right.
This is how I do it. First, I crash in the fermenter to 40F. Then I run a closed transfer under mild pressure into an 02 purged keg around dinner time. Next, I purge the headspace, repeatedly. Then I pressurize it to 40psi and toss it in the fridge with no gas line attached. I wake up at 3.30am on weekdays, around 5am on the weekends, so I'll hit it with an additional 20psi when I wake up the next day--or another 40psi if it's something that needs a lot of carbonation. After work on the third day, I'll quickly pull the PRV to assess where the beer is, then hook up a line and pour a pint. Typically, I'll get clear, carbonated beer that needs additional gas to throw a head. Another shot of 20psi will achieve that goal. For the first week, you'll find it necessary to serve the beer under extra pressure to get it to throw a proper head, then use the PRV valve to back off that pressure to keep it from over-carbonating until your next session. After the first week, it's really easy. You just start pouring, give it a little dose of gas (maybe 5psi--I tend to keep my regulator set to 20psi and pulse gas into each keg as necessary) if it needs it and then mostly leave it alone, a quick squirt of gas every few pints should keep your beer pouring sweet.
It sounds complicated, but it isn't. Best of all, you never have to worry about leaks and cylinders lost to leaks...aside from leaky kegs, but you can't lose too much CO2 from a leaky keg that isn't attached to your cylinder.
Again, the advice offered above by others is far superior, just do that! But I find the process I've outlined much more rewarding. If this sounds interesting to you, there is a learning curve involved in this. You'll figure it out soon enough, but you're going to have to put some work in.
