In Wisconsin you have to take a real estate class, it is either 10 or 15 weeks, three hours twice a week. After you finish the coursework you get a certificate. Then you apply to the state to take the real estate exam, you have to supply the number of your certificate to be authorized to take the test and it has to be within a certain time period after you finish the coursework. All told, you should be able to get your license in WI in 6 months or less.
Every state has its own rules, so you might want to check on your state's .gov website.