What to do if I want to set up janitorial services company?

A limited liability company (LLC) and a subchapter S corporation (a type of "inc.") are essentially for the same for 90% of practical purposes: they both insulate the owner(s) from personal liability for business debts (unless the owner(s) personally guaranteed the debts; and except for a few specific exceptions, like debts arising from a tort the owner personally committed, like running someone over while driving a company vehicle, or certain tax debts); they are also both "pass through" entities in that there is no corporate income tax, but rather profits or losses "pass through" the company to the owner(s) and are taxed only on the owner(s) income taxes. A subchapter c corporation is a totally different animal in that it sets you up for double taxation (paying corporate taxes; then being taxed on your income from the company, too) and is best for larger companies that need a more formal structure.

Between an LLC and sub-S, an LLC is slightly easier to administrate and set up (less paperwork) and is usually the better choise. A sub-S might be better if you anticipate you might later sell some part of the business (i.e. some shares)--that's somewhat easier to do with a sub-S than an LLC.

You should set up with an LLC or sub-S; register the business to do do business in your state (go to your state's governmental website for forms, instructions, etc.); buy insurance (even with the LLC or inc., you also want insurance); and, if you are going to have employees, when you do, make life easier for yourself and let ADP or someone else like that handle the payroll.