Among the items you obtain from slain foes, you may find pieces of equipment – weapons and armor which will increase your combat effectiveness. 

In order to wear a piece of equipment, your character must meet or exceed the requirements, which can include any or all of your character class, your level, or your statistic levels. You must also have a free equipment slot available – every piece of equipment corresponds to a particular slot on your character’s body, and you only have one slot available for most types of equipment. However, your character can wear up to two earrings, two bracelets, and a sum total of four rings and necklaces. 

You can’t wear a piece of equipment if you haven’t met its requirements. If you are wearing a piece and cease meeting its requirements, the piece will become non-functional (it will confer none of its benefits to your character). 

If your character can wear a piece of equipment when they obtain it, and doesn't already have something else equipped in its slot, it will be equipped automatically. Otherwise, the equipment will be placed in your inventory. You can equip a piece of equipment by clicking it once to place it on your mouse cursor, and then clicking on the equipment slot in which you wish to equip it. You can also right-click on a piece of equipment in your inventory to equip it. If there is already a piece of equipment in that slot, it will be swapped with the newly equipped piece, either in your inventory or on your mouse cursor. 

Some pieces of equipment are exclusive with others and cannot be equipped at the same time. This can include different stages of items that can be upgraded, or certain crafted accessories. 

You can compare a piece of equipment with what you already have equipped by holding the CTRL key while your cursor is on top of the item. You will see one or more numbers, which compare the relative strength of the equipment. Green numbers means that the unequipped piece grants a higher bonus to that specific stat, whereas red numbers mean that the piece you are wearing grants a higher bonus. 

As characters reach higher levels, there’s a lot of nuance and complexity involved in equipment selection. To start, just keep and wear pieces which grant the highest attack damage and defense that you can get. 

As you gain more equipment and more varied skills, you may find it beneficial to have two sets of equipment which you can switch between rapidly. In your inventory screen, next to the equipment slots labelled with a sword and shield (your main hand and off hand slots) are two tabs, which you can click to access your secondary weapon slots. You can equip two weapons at the same time, though you will only gain any benefit from your active weapon. You can switch which weapon is active be pressing TAB. 

You can also equip an entirely separate secondary set of equipment, besides your weapon. You can access both equipment sets with the two Equip tabs on your Inventory screen, and press SHIFT-TAB to swap them. If there is nothing equipped in a secondary equipment slot, it will not be swapped out when you switch between equipment sets.