Healing is a bit different in Resident Evil 6 than it was in Resident Evil 5.
Your character is now fully addicted to pills now (awesome!) and herbs need to be combined into health tablets before you can use them.
Check out my other article if you’re having trouble figuring out how to mix herbs into tablets.
Basically you just need to combine some herbs in your inventory to create health tablets, then place those tablets into your case using the drop down options when you click on them.
Once the health tablets are placed into your pill case, they are removed from your inventory and you can use them.
Look on your HUD in the game once you’ve done this, and you’ll see a number above your health bar, which is the number of health tablets you currently have in your pill case.
As long as you have a tablet in your pill case, you can press RB on the Xbox 360, or R1 on the PS3 to use one of the tablets to heal yourself for one bar section per tablet.