Press I (default) to bring up the inventory. When you are at a lodge or near a tent, you can access your lodge inventory. The items on the left are what is available for adding to you field inventory. The number shown next to each slot is the key that is configured for selecting the item in the game. Key bindings can be changed in the Options of the game.
In the lower right corner is the capacity meter. Depending of whether you own the upgrade "Increased Capacity" or not, you have 10 or 20 units of capacity available. Every item you equip will take up a certain capacity. Hovering over the (i) symbol will display the capacity cost. Clicking the (i) symbol will open an window with more information about the item.
Weapon slot 3 and item slots 8 and 9 are not available from the beginning. They must be unlocked by the player. Find more information in the Hunting Aids section.
Equipping Items: Video
Your hunting inventory consists of a number of slots.
Simply click on a weapon slot and select a weapon from the list.
After a weapon was added, the according ammunition will pop up and you can select which you want to assign.
Click the scope slot and equip your gun with a suitable scope. During the hunt you can move the scope back and forth between the weapon and the "Unequipped carry items" slot at the bottom.
Repeat the same for the second weapon if needed.
If weapon slot 3 is available to you, repeat the same for the hand gun.
Any equipment you want to bring in addition to what you have added to the slots, you can simply pull from the left menu into the "Unequipped carry items" slot at the bottom. Keep an eye on that capacity meter in the lower right. If you cannot add any other item that is important, reduce what is already loaded to the field inventory.
At the top of the inventory overview, click the [Clothing] button. Click on the body part slots to equip clothes.
Your clothes do not underlie any capacity limitations.
More clothes can be bought in the store: http://www.thehunter.com/store/?category=0