If you would like to enter the US to visit different Universities as you consider the schools you might want to apply to, you can do so using the B-2 Visitor Visa. This visa type will allow you to enter the US for up to 6 months at a time, but you cannot begin your studies with this visa type. Please plan to leave the US again to apply for your student visa before formally beginning your studies in the US, though if this is impossible please consult ISSS for advice on other options.
Citizens of some countries can enter the US without a visa for short visits. Check here to see if you are eligible for the Visa Waiver program.
For those that need a visitor visa, learn the requirements and process to apply here.