At the bottom of people's details on the left hand side are 3 icons, a green circle, a grey scale and a triangle.
You click on the scale and it reps. You can add a comment and your name if you wish.
going O/T more now but you will find that you can only give so much rep in a day (think it's 10?? I frequently use mine up!) and you have to spread the lurve around, it won't let you rep the same person until you have repped others.
That's what I rep for Elle - when someone says something helpful to others, or when they make me smile or when they need a perk up or for a cracking recipe tip.