- marry him
- file form I130 (immigrant petition for alien relative) with the office of the US citizenship and immigration service
- have him file form I485 (application to adjust status) in the same package
- have him file form I765 (application for permission to accept employment)
- have him file form I131 (application for travel document)
After that he will get his work permit in 3 months and his conditional green-card within 2 years or so. After 2 years, you both have to go for an interview and proove that you are indeed married. If you satisfied the immigration officer that your marriage was not a sham just to get the GC, his 'conditional' greencard is converted into a permanent one.
This of course is a very simplified description of a long and somewhat more complicated process. There are other options, depending on where is is from it might make more sense to go through the US consulate in his home country using fiancee or spouse visas (K1,K3).
Check out the 'family immigration' subforums on this site.
http://www.immigrationportal.com/forumdisplay.php?f=39 There is plenty of useful information to be garnered. Don't be too frustrated. Internet forums like this tend to attract the frustrated customers of USCIS. For every person who gets jerked around by USCIS, ther are probably 10 who breeze through the process without major hickups.
If you are smart enough to file your own taxes, you could probably do the entire process yourself. If you want guidance, you can hire an attorney to do the work for you. It saves you from filling out the forms incorrectly, but it will set you back a couple of $1000.
(I assume you are a US citizen. If not, all the abovesaid is irrelevant)