Hmm, I never tried to use this things because spammers are around and wouldn't leave me in peace. But let me try helping you out..

On top right side there's your name, on my case "DK" Click on that and it'll pop out a little window with tons of options about you and your account, etc.. Click in "Personal Details" and then look on the left side a column of options and select "Steam Integration" and associate them.. Good Luck!