Recently a user in the irc channel I frequently visit had some trouble understanding this, so I decided it would be a simple thing to show that others could benefit. Using GetProcAddress is really quite simple, but the way you declare the function you're getting often looks alien to a beginner.
This is how you do it in C++ if you were to try and get the address for MessageBox. First you may find it easier to make a typedef that will be the "type" of your function (much like as if it were a variable).
Really this is just the same function prototype of MessageBox, just organized a little differently. I am going to go ahead and assume you've already used LoadLibrary and jump right into GetProcAddress.
And that's basically all there is to it. Just make sure when you are done that you free that library you loaded. Also if you made your own library and have trouble figuring out what the actual name of the function is after it was linked into your DLL there are tools you can find online for that. Sometimes your function names get padded with extra stuff, which I don't think happens if this were just C. This is not the case usually with any functions you want to get from Windows libraries so you are usually safe just using the name you know it is with A or W as a suffix if needed.