spikes...

Spikes, Stealth Rock, and Toxic Spikes.
I see them used in a lot of battles.
People even have rapid spinners to counter these moves.

But I really don't get it? I don't know if it's just something you add in, or it's a basis for a whole team? Also, is it something to worry about?
What's the deal with spikes?

They are a counter for switching, if someone has Spikes, Stealth Rock or Toxic Spikes on their side of the field they will have a serious disadvantage because switching to a counter is a large part of competitive play.

They will also prevent Focus Sash from activating.

Adding on to what Ghost42 said, the passive damage done by Spikes, SR, and Toxic Spikes can also help in the process of KOing certain Pokemon. It puts just within the range of a KO, this helps serious competitive players(who often times calculate near KOs to within the range of 1% or less) to get rid of specific Pokemon their team may have trouble with. For example an Adamant 252 Atk EV Lucario w/ Life Orb can do around 96-112% damage to a Bronzong after 1 Swords Dance with Close Combat, but with the 6.5% damage done to it by Stealth Rock, it's a sure OHKO, if it switches in on it.

So yeah, you don't usually need to worry about Spikes, etc. unless you have a lot of Pokemon that are weak to them in your team or they cause problems for your team , in which case you should probably consider a Rapid Spinner, or better yet make a new team, because Rock is a common attack type.

Spikes have a good advantage.When you use them they have great damage.So if you have someone like onix or geodude or even cranidos teach them spikes!

Spikes are good when they aren'y used on you.

I should teach my Rampardos Spikes. But when somebody used spikes on me in-game I didn't have to worry. You know why? It is because I never had to switch out. Yes I was that good in-game. Never tried online competitive though. So I will be glad to try it.