A DDOS is normally when a botnet continuously request your server, overloading it.
You can use anti-DDOS (deflateddos)software to minimise the effects of a DDOS, if you do find yourself in a DDOS attack the best thing to do would be:
1. To sit it out.
2. To shut down your server and sit it out.
In terms of 'fixing', a reboot should get it all good again, but if you leave it on during the DDOS make sure the active log files don't get too big or apache will start behaving randomly.
I'm new to this. I had servers for 7 years and never had an attack. I was never prepared and I have not idea what to do if it happens.
If it's not DDoS and just DOS, it can go on forever or will it stop after a while. One hour wouldn't matter but if it takes more than I should be able to do something, right?
Sorry, I'm totalyy new with security.