What does it mean when someone says to you step and fetch it?

Stepin Fetchit was an African American actor who was very well known during the early-middle part of the last century. In fact, he was known enough to have been considered an actual moviestar--if black people were taken seriously enough to be thought of as stars that long ago.

His is one of the most well known stories of the terrible characterizations black people were forced into if they wanted to act onscreen.

In his lifetime he noted that his name came from that of a racehorse upon which he bet and won a considerable kitty; on the other hand, it's most likely if someone uses this rather terrible term today it is meant in racially degrading manner.

Very sad. There is a lot more information available online about this time, this man, and this error [and others similar] made by the movie industry--not to mention the society for which that industry created product. All you have to do is search.