Please explain Data Usage to me? - 1

I have an ATandT iPhone 4S. Every month I'm not allowed to go over my 12GB data usage plan, and if I do I get charged for it. Well, today my mom got mad at me and yelled at me over how my phone bill was about 100 last month, and that it was because I had gone over my monthly data usage plan.
Originally, my mother told me "data" was only the 4G aspect of my iPhone, but now she has told me it is everything on my phone (texting, 4G, using apps, etc.). This seems like a bunch of bologna to me because my mom, brother, and sister's phones all aren't charged this way (they have all had their iPhones for longer than I have).
So, can someone please explain to me exactly what "data" or "data usage" is so I know what I need to limit doing on my iPhone each month?

Can I use the Spotify app for free without upgrading to Premium?

I just got the Spotify app on my iphone last week and it said I can try a 7-day free trial, so ofc I chose that. Now those 7 days are up and Spotify is telling me to upgrade to Premium in which I pay per month. I can't play any of the songs I saved unless they re on shuffle. I can't even play the songs I looked up from Search. My Spotify on the web works fine.

IIm wondering if this is normal because my friend got the Spotify app on her iPhone around the same time I did and she doesn't have the Premium Spotify, yet her app is working fine and she doesn't have to pay. Anyone know what's wrong or how to fix this?

Is an iPhone 4 for $33, worth it?

16GB, Black, Full set, iPhone 4 is available for sale in a Sri lankan shop. I'm from South Dakota, not Intrested in iPhones but I heard that one of my friends bought an iPhone 4 for $99. Just wondering whether I should buy it or not. By the way the Sri Lankan phone prices seems to be way cheaper, Just can't believe it. I got an s6 edge for just $250. Back to the topic please tell me whether I should buy the iPhone 4? I ll be coming back to the States next week.

Problem with Wi-Fi on iPhone 5?

I have an iPhone 5 and it's really bad with connecting and staying connected to Wi-Fi. I know that the signal reaches upstairs because everyone else is able to use it fine and my laptop, which is usually in the same room as my phone, works just fine.
Whenever I go to a friend's place, the same thing happens. Can someone please help me? It's extremely frustrating.

A problem with the virtual reality headset?

I just received my virtual reality headset but i have a few problem with it
First when i puted a photo in google street viewer i see the photo not clear. Its like what i see with the left right is above the other eye and it will need me a while to see the real picture and when i give it to someone else he see the photo not clear and suddenly he see the real photo. And for a video it does not become clear at all
second thing when i see through it i see the black box of the headset and it never be a good experience like they say cause when seeing The box it feels like looking through a box
So i'm i missing something or its like that for everyone
the name of the headset is " reim "
The phone i'm using is iPhone 4s

What to do with shattered iPhone 6?

Today my phone took a hard fall and shattered, sadly. But luckily the phone still works but the bottom half of the screen is covered with cracks (think black ones) everywhere but the top only has a few thin cracks. I can't get a new phone for another 6 months so is it worth getting my screen replaced or should I replace it myself or is there a special screen protector that I can use to help it out. Right now I threw it in my old lifeproof that I was stupidly not using so it won't cut my fingers, but is it worth getting it replaced, or is there a screen protector that I should try that will fix the cracks? Thanks to anyone who helps me and sorry for my terrible grammar

How to get a multiple voice effect?

IIm recording a song on a multiple track app on my iphone but I also have cakewalk, garageband, and audacity. Is there any way to get the same sound as recording the same vocal track multiple times without actually doing so? It's extremely difficult to sing exactly the same each time.