Need help about SIM card.

So, I was messing around my phone, and I opened the SIM card thing or whatever. And there was no sim card so I just put it back and now it tells me I don't have a sim card. But I never had one in the first place. Know I have no data, phone number and stuff like that... I don't know what to do. I'm using T-Mobile if that helps. Please help!

You probably had one and it fell out. A TMobile phone won't work without one. Bring the phone to a TMobile store and tell them what happened. They shouldn't charge you for another card.