How to find out what carrier my Iphone 6 was bought from?

I have recently received an Iphone 6 but how do I find out what carrier it was bought from. The person I got it off has no idea and neither do I but I need to know in order for it to be unlocked. I ve tried using my O2 sim inside it but it comes up with SIM Not Valid and the message that comes up when it s locked which rules out O2 but I need to find out which carrier my phone was bought from so I can unlock the Iphone and use my O2 sim in it.
Thank you for any help xx

How to get my photos all in focus?

if i take a picture of something on my dslr one part will be focused depending on the distance but i want it all to be in focus like how the cameras work on iphones, if you dont focus it it ll all be in focus. How do i do that on my dslr.

My iPhone 6 will not charge?

My iPhone 6 that I've had for 3 months or so stopped charging yesterday, I've tried every wall port and different cables. When i plug it in it says something like "this cable is not able to charge this phone reliably". What could this be?

My grandma doesn't care about me when I was sick?

To be honest she never hug me kiss me or anything. When I was sick she only give me pill and nothing else. There was a time where a big ball thing in my nose and it causing breathing problem and ear ache when I go to the doctor and it was huge and come back home(after fixing it and some medicaton) it cost us 50$ and she said it was a waste of money and she said it was the headphone (how the **** can a headphone do anything with breathing problem) and now I have a lump at my back teeth And it not wisdom teeth because I'm too young and I say it she say don't be a smartass and I have problem eating and sleeping for 4 day I was shock I want to go to the dentist (usually I afraid of dentist but this could be cyst and abcess ) it usually cost below 100$ to fix but I don't have health care if I have I will go to the dentist myself and the most shocking thing is that my other cousin she give her money on them more than me (for me I don't want her money all my phone and stuff are my parent money and i live with my grandma) example my aunt already have 1000$ motor bike and she want to sell it and buy another one for just a brand new one and she want a plastic sugerly I'm not American for attractive to be honest if she do it it look the same. For me I have a lot of problems like my parent give 50$ to buy a new hardrive and she keep it and not fixing my laptop and it was my parent money for me to fix it and she give my mom wedding ring to my cousin mom and she kick me out for an iPhone

Why doesn't my iPhone 6 connect to wifi?

So when I connect to the wifi in my house it automatically turns off and uses data if I go on safari, on Netflix, and even Instagram. So I decided to try it on my friends phone & when I tried use them on her phone, the wifi stays on and it doesn't turn off and use data. Also, the wifi isn't bad where I'm using it, on my phone it has 1 bar but on my friends phone it has 3. So I don't know what the problem is and why it isn't working.

Where can I get a cheap iPhone?

I actually broke my phone yesterday and I'm in need of a phone ASAP are there any online sites / stores where I can get a cheap iPhone?