This small pot of oil is intended for optimising yo-yos which require a 'bind' (i.e. are 'un-responsive).

Small particles of dust or dirt can occasionally get lodged in your yo-yo bearing's internal mechanism - this oil will help alleviate the problem and return your bearing to running quietly and smoothly. Using this oil will also increase the lifespan of your yo-yo bearing.

Please note that oil may cause a bearing to run slightly slower than a 'dry' bearing, but the difference is barely noticeable unless you're consistently throwing non-stop, multi-trick power routines.