How to record while on an app?

Like If i want to record me playing a game or me in notes, how can I do that? I have an iPhone 3 btw. Do I need an app? Tell me apps I can use, any solutions.

Can a battery be replaced in an Iphone 4?

My battery is having to be charged all the time now with very little use. Can I have the battery replaced, and if so where would I go to have it done. Is it expensive?

What do people use to take selfies of themselves taking selfies?

I have to help someone take a good selfie for her profile but I can't exactly explain it. As far as I know, the front view lens only captures you and your background and the rear facing lens on the back of the phone takes a picture of what is in front of you, such as a landscape. That said, using an iPhone 4, how is it possible for someone to take a selfie that looks like there's someone taking a picture of them while they're doing it.

Can I retrieve my old text messages?

Okay so I deleted a few text messages that I shouldn't had deleted. I have an iPhone 5c but i don't know if it's possible to retrieve deleted messages if yes how?

Free music download for iphone 4s?

I can't remember what its called but I had this app that let me download 15 songs without having to pay but i accidentally deleted it and I can't for the life of me find it again. All I know is it downloaded the songs off of youtube and put them on the app so i could listen to them without using data and it had a logo that was a white square with a blue star in the middle. Please and thank you.