Do i need someone to put in my sim card or do it myself?

I have a tmobile iphone 5 I just bought from somebody. Do I just put my tmobile sim card(I cut it already so it can fit) in it and itll automatically work with Wi-Fi and all that… Or do I need to go to the tmobile store and ask them to do everything and put Wi-Fi and all that on it?

They don't need to do anything if you're just wanting to use it on Wi-Fi. You just take a paper clip and it pops out on the side of the phone.

You could do it yourself. Just eject the SIM tray, stick in the SIM & put it back in. Done.

Wi-Fi has nothing to do with the SIM card and or T-Mobile for that matter.