Welcome to the forum, babyboy.
Like any web-based transaction it's best to know who you are dealing with. I mean, how do you even know that the person you are dealing with is the owner of the domain. Just because I may have a corporate sounding email address for ... say ... mail.com, doesn't mean that I own the domain name.
On the other hand, I have purchased lots and lots of domain names for $25 to $400 where I just sent the money and hoped and prayed. And I've only been screwed about 2% of the time - so that's not bad. (Curiously, on the cheaper domains. )
Obviously, if you are buying the domain for a lot of money (like $10,000), you would want to use the services of an escrow company like www.escrow.com or www.sedo.com to insure your investment.
But basically, the seller unlocks the domain at their registrar, and the buyer initiates a transfer from their registrar (paying for an additional years registration to the registrar for the transfer). Or, many registrars, like Enom, allow the name to be "pushed" by the seller into the buyer's account for no fee (since it is all internal).
Then, like empresasdehosting suggested, you need to change the whois contact information immediately and LOCK the domain to prevent it being transferred away from you. Whatever you do... NEVER get talked into releasing YOUR account login details to anyone (like the seller claiming he needs the info to initiate transfer) or you may end up losing ALL your domains.
If you plan on buying just a few domains, you might checkout www.NameCheap.com .
FYI ... I've bought some great domains over the years down in the advertising section right here on WHT. You also might search for an available domain. I can usually find a decent domain name for almost any business in thirty days if I look at the expired lists on www.JustDropped.com ; the expiring lists on www.NameWinner.com ; the namespinner on www.whois.sc ; and sometimes (though not too often) www.NameBoy.com
You may delay, but time will not. --- Benjamin Franklin