To heal yourself, cycle through your weapons/goodies til you get to the first aid pack. Then when you're holding it, press the fire button until the circle fills up. On the PC you can use the mousewheel to cycle through, on the 360 I think you hold the yellow button. But it's the same button as if you're switching from main weapon to pistol.
Glad you like it - It's very pick up and put downable - for me that's a must these days, I'm not a young man any more and don't have the time to go too indepth into stuff:)
Fran
PS - I'm getting older, but I'm still not as old as 20mm;)