The equipped effects menu can be used to choose which potion effects players (or other entities) should get while holding or equipping a custom item in the right slot. If you just opened this menu and clicked once on the 'Add new' button, it should look like this:

• Clicking the 'Cancel' button will take you back to the item edit menu you came from, without keeping any changes you made here.
• Clicking the 'Apply' button will keep the changes you made and then take you back to the item edit menu you came from.
• Clicking the 'Add new' button will add a new potion effect row, which you can thereafter adjust to your needs.

Furthermore, there is a row for each potion effect currently present. Each row has the following buttons and fields:

• The red cross on the left will remove the row (and its associated potion effect).
• The effect button displays the currently selected potion effect of the row. Click it to change it.
• The slot button displays the currently selected slot for the potion effect. The potion effect will only be given if the custom item is held or equipped in that slot. Click this button to change the slot.
• The edit field on the right of 'Level:' displays the level of the potion effect. Increasing the level will amplify the power of the potion effect.