iPhone crashes too much!

First try a reset - Press the Sleep/Wake button and Home button at the same time for ten seconds until the Apple logo appears. Note: No data will be lost

If the problem persists - Restore the iOS with iTunes on Mac or PC, first from a backup and if you still have the issue(s) Restore as a new device with iTunes.

If all fails to solve the issue(s) you may need to have the device looked at by the folks at the Apple Store

You might also look at whether the available space on your phone is almost full. If it is delete some apps, photos, movies or other stuff to give your iOS some breathing room.