In Deus Ex: Mankind Divided, all the items and weapons you pick up will be sent straight to your inventory. You can check your inventory by bringing up the game menu, and heading over to the inventory tab, which is indicated by a gun icon. To use an item in your inventory, simply hover over it and select them item, and then use it from there. If you want to equip a new weapon, select it, and choose the ‘equip’ option that appears after you select it.
Consumables like the biocells and hypostim injectors can be accessed if you hold down the V button on PC to bring up your item wheel. On the left of the item wheel, you’ll see a separate slot for your biocells, and the hypostim injectors will be on the right. Clicking on either of these items will allow you to use them up immediately. This is a lot more efficient than heading to your inventory tab to use them. The biocells will charge you up so you can start using augmentations again, while the hypostim injectors will restore your health if you take damage.
Make sure to clear out and organize your inventory from time to time. You can run out of space pretty easily in Deus Ex: Mankind Divided.