In Ghost Recon Breakpoint, healing is mandatory if you want to stay alive. After taking damage you can heal yourself with different types of items. Two items that you can heal yourself with are the Syringe and the Bandage. Both items will be in your item wheel and can be accessed through there.
To pull up the item wheel in Ghost Recon Breakpoint you can press and hold the RB/R1 Button. Highlight either the Syringe or the Bandages with the Right Stick and this item will be equipped for quick use. Once you have the item equipped you can then use the LB/L1 button.
The syringe and the bandages each have different uses. The Syringe heals 100% health and removes some injuries. Syringes are finite and you will only be able to use one if you have them in your inventory. Syringes can be crafted at Biouvac. Bandages are infinite use and heals all injuries.