Where Do I Have to Buy the Domain Name From?
You can use any domain from anywhere. You don't have to register it with a domain parking company, nor move it. So you are still free to buy a domain from a cheap provider.
How Much Money Can I Make From Domain Parking?
I'm afraid that is a "how long is a piece of string" type question. Nobody knows. But if you develop a knack for it, it can certainly pay well and once you've got your domain parked (which takes just 2 minutes once you're registered) you don't have to do another thing!
But let's look at some facts
There are two types of domains: A completely new domain - and - an expired domain.
Ever surfed the Internet, clicked on links and found the website is dead? These are expired domains. They no longer exist, but, other sites link to them.
A new domain, on the other hand, has no existing inbound links. And you won't get an inbound link to an empty page/site.
Most of the easily guessable domains have gone, so you are unlikely to be able to buy a domain name that many people will just type into the address bar to find out if it exists. This means any new domain you register is unlikely to have much traffic going to it, if ever.
But, if you can buy an expired domain, then it may already have links into it from other sites. This means that the domain you bought is far more likely to attract passing traffic!
The trouble is, how do you find expired domain names? And how do you make sure you buy them the minute they come available?
Companies who provide domain parking can also get you access to lists of domains which are due to expire, and you can even pre-order them to try to be the first to register them the minute the domains become available. Most people who are making a living at parking domains have taken their time to build up a number of new and used/expired domains. They didn't sit down in an afternoon and think up a bunch of names and just register that lot.
It's worth looking into - and if you have any existing domain names you've registered, why not park them for now and see what happens?
The Bottom Line
If you've got domains just sitting around, it's worthwhile parking them just to see what happens - or - if you are a domain name speculator it would be worth looking into recently expired domain names or those which will expire shortly. I certainly have a couple of friends who are making a good living at domain parking, and I've just parked my first one myself, just to see.