Here are some of the things you need to do for your friend.
1. You’ll will need to first choose a business entity type.
The Secretary of State's office "offers useful information in this area and the ability to perform many required filings online" at the following website;
Missouri Secretary of State Robin Carnahan :: Corporations Division :: Starting a Business 2. You need to Obtain a Federal Employer Identification Number
Your friends business may need a Federal Employer Identification Number (EIN). which you can do it online with the IRS EIN Form. Here is an IRS link that would enable your friend to apply for an EIN#.
http://www.irs.gov/pub/irs-pdf/fss4.pdf 3. Register for a Tax Identification Number and an Unemployment Tax Number
If your friend plans to either sell products or hire employees, he will need to register with the Department of Revenue. This can be done at the "Online Business Tax Registration website
https://dors.mo.gov/tax/coreg/index.jsp, which allows taxpayers to enter the information only once and have it used for several registrations such as the following tax types as shown below;
Sales Tax
Vendor's Use Tax
Consumer's Tax
Withholding Tax
Unemployment Tax
Tire/Battery Fee
Corporate Income/Franchise Tax