renting questions

hi! I am moving to boston in july to begin grad school. i have never lived in boston and have never rented before, so i would really really appreciate any advice!
1. for renting amenities apartments, how quick is the turnaround once you apply for a unit online? are you pretty much guaranteed to get the unit if you apply online? or should you apply to multiple? and do you need a realtor or can you apply directly through the website?

  1. for other housing options like brownstones, what should be your next move once finding a place you like on apartments . com, zillow, etc? should you call the phone number given directly? what is the likelihood of getting the apartment once applying?

thank you!!!