click the green flag next to ones name to rep.. do stuff like host mods or help reople to get rep

You have to have rep to rep some1 the green flag on the bottom right corner of every post is how you rep some one
It takes 100 rep points to gain one rep power

To rep someone : You will notice a Thanks buttom, a Red Flag and a Green Flag.
To positively rep or negatively rep, press the Green Flag next to the post on the bottom right.
You can give people + rep or - rep, determining what you need to do.
To gain rep : Every 25 posts you will gain 1 rep power, to see about te Reputation System, go to the Account tab then Reputation.
People can also rep you points, every 100 + rep points you achieve you will gain +1 rep power.
Hope I answered all you needed

You rep by pressing the green flag

You gain rep power by posting

i just gave u rep just to welcome you

People choose to rep you if they want to. Also you click the Green Flag on the bottom of someones post and it will allow you to +Rep them or -Rep them. But you have to have rep to - or + rep someone. Also you receive rep after a certain amount of post which you have posted. I think the first rep is when you get 24/25 Post. You can also then a topic by clicking the "Thanks" or the "Thumbs Up" or if the post is unhelpful you click the "Unhelpful" Button which is the "Red Thumbs Up" button.