To send credits click on the Credits icon, on the right of the screen at the top of your inventory. :)
Or clicky here: http://www.swcombine.com/members/credits/
It'll take you to the screen where you can send credits to others. Enter their handle/username, the amount of credits and a reason (if applicable) for sending eet, ayah.
Edit: Double check your details before sending (triple check even) as there is no confirmation before sending teh credits, ayah.