How do I register start up business?

First you decide whether you are a sole proprietor, LLC, or corporation and you will need a EIN number or TIN number with the government. Go to http://www.irs.gov/businesses/small/article/0,,id=102767,00.html . You will need to register your company on https://orca.bpn.gov/ and lastly you will need a DUNS number which you can find at http://www.dnb.com/us/duns_update/
If you want to register your business with the Federal government you need to go to bpn.gov and register on the CCR system and would also suggest registering on vetbiz.gov as well and see if your company qualifies at http://www.vetbiz.gov/vip/eligible.htm

Hope this helps