Ordered an iPhone 6 from the Apple website for TMobile, how do i set it up when i get it?

I recently ordered an iPhone from the apple store for my carrier which is Tmobile. It is my first iPhone ever and i was wondering how what are steps to activate it and make it my primary phone? I have the galaxy s3 right now. Just looking for some detail on what i meed to do. Do i need to take it to a tmobile store or can i do everything myself?

The phone will come with complete directions to "set it up", the SIM card should be ready to go with your new number (if this is a second line) or the current number if this is the same line.

You will need to keep the old phone OFF and remove the SIM, is this is the same number. But again that should be in the directions for the phone. If you want to take it to a T-mobile store, you can, but the process is very simple.

You can do everything yourself.
You need to create an Apple / itunes account in the process.

Basically, just go through the on-screen instructions and it will take you through step by step.

Put in your SIM & go through the initial set up. Very easy. It would be activated during this time.

With iTunes on your laptop, the sim, and the phone, you can do all of that yourself. It has guides to help. Best luck.