Posting in the wrong section isn't going to help!
Here's the official tourism website:
http://www.mongoliatourism.gov.mn/lang/2
I'll happily try to work out how you can get there - and what the visa requirements are - if you'll say where you're starting from. (This is a UK-based website but people posting here in the early hours of the morning are often in the USA. It would be pointless for me to type out all of the travel options from London if, say, you're in Chicago!)
Please post again (in the Travel section) telling us where you are and exactly what it is you need to know.
Chris