Both mean the same. No particular reason why you would you use one or the other. But may be can be a little bit difference. "Have to" could be used when you want someting, but it can waits. "Need to" could be used when you really need to do the action. It is an obligation.

I can't think of a specific description unfortunately but one example of the difference could be going to the washroom (all I can think of sorry). Having to go to the washroom would be when you feel you have to pee but you don't have to go right away. Needing to go to the washroom would be when you feel you have to pee and can't wait/have to pee imediately. In this situation need is more dire than have. The difference between the two is often like this. Hope this helped.

"I have to do something" means "it is necessary for me to do it". I have to go now, my plane leaves early in the morning. (if I don't go to sleep in time, I may miss the plane, so I have no other choice but leave now) "I need to do something" also means "it is necessary for me to do it". I need to work harder if I want to get a good job. Hope this helps.