My phone keeps hanging and it will just go off on his own please why?

@oluchiezen99729 try a reset first. Just make sure you have a copy of your files/pictures/contacts since you may lose all of those. Also know your passwords etc. For a hard reset, use information from sites like this and many others.

If that does not work, you want to replace the battery as well as check the power flex and the flex from the charging board to the main board. Since iFixit does not yet have a guide for that, Use something like this video

While you work on your phone, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.