Highlight the Item/Item(s) you wish to remove.
If you wish to remove a single item simply click on the item once.
If you wish to remove multiple items you will need to highlight the items you wish to remove. To highlight a list of items click at the top of the list, press the Shift key, and click at the bottom of the list. To highlight a variety of items in a list hold down the Ctrl key and click the items you wish to remove.
Right-click and select the Delete From List option.
Manually adding items/albums to a playlist
How to remove a file from the Media Library