I was reading the Wiki on how to make an experience system, but got more confused. I am trying to do a RPG, but I'm trying to learn how to do a proper exp. system unlike with only kills.

I think that this doesn't work, right?
Players - xxx
Condition - xxx kills one xxx at xxx
Action - add one custom

And this is how to do it, right?
Players - xxx
Condition - xxx accumulates exactly xxx killscore
Action - add one custom
- subtract xxx killscore
- preserve trigger

Is there an easier way? Do Hyper Triggers have to be used?

You might want to look at this: http://www.staredit.net/wiki/Kills_To_Cash#%22Perfect%22_kills_to_cash

Hyper triggers are not needed, but definitely recommended as they speed up the process and depending on the method reduce errors caused by splash/multikills considerably.

Your 1st method:
This can work, but you'd need 1 trigger for each number of kills possible. If you're not afraid of using a trigger duplicator go for it. It would look like this:
exactly 1 kill: add 1 xp
exactly 2 kills: add 1 xp
exactly 3 kills: add 1 xp
... etc. (not preserved!)
This makes especially sense if there aren't unlimited enemies on the map, e.g. only preplaced, not spawing.

Your 2nd method:
Well there is no easier way, this is already very easy. But there's methods that are less prone to glitching. Basically you can use any method in the "kills-to-cash" wiki just that you don't add cash, but experience.

The perfect kills-to-cash method works flawlessly, but could have trouble keeping up if you have a lot of killings going on all the time and you need a computer player that is not allowed to kill any units that the player(s) can kill.

i just use death counts, my rpg uses an experience system like the game fable, where you dont level up but you get experience points to spend on skills. after a certain number of death counts you get one experience point for the skill you've been doing.

for example after killing a monster it would add one death, once you have 100 deaths it resets and gives you an experience point. Thats my idea.

That doesn't work in multiplayer, as you have no way of detecting who caused the death (aka killed the unit).