This menu tab is where you craft items using resources in your inventory. Simply click on the items you need to craft and it will show you the material needed at the bottom right of the window to craft the item.
Each item is sorted in its own category and you can click these categories to find the item you need to craft much quicker.
Once you find the item you need to craft and got the resources in your inventory, click on the craft button.
You can also find information on what items you can get other items from when scrapping/recycling them by clicking the small recycle button on the thumbnail of the item you clicked on.
Please note that some items will not be craftable unless you found one in a raid and recycled it to get the blueprint for it. You may also stumble across books to learn from.
As you are raiding you will come across berry bushes. Collecting the Berries off these bushes will allow you to craft Potions. These will be key to your survival in higher tier raids.
When you begin drinking these potions, you can swap off to your weapon and continue the slaughter.