Every operating system, be it OSX or Windows has its share of problems. It's usually due to installed software or hardware. If you have a problem after install, take it to the Genius Bar at an Apple store. I took my iMac in last Friday because it was mis-behaving...not related to El Capitan as it turns out, and they worked their magic and it runs fine. There was no charge and they spent 2.5 hours on it. This is on a 6 year old iMac. You can sign up at www.mac-forums.com. They have answered a lot of questions for me.
U.S.C.G. "Making sure the Navy doesn't get lost since 1790"