How to put ''Search Keywords'' to your story?

Hey, this may sound stupid, but how do you put search keywords to your story. It always say that they are invalid even though I put them exactly how it was in the example. Help please? :confused:
I didn’t found any forum discussions that speak about these.

It should be something like this:
Love, cool, summertime, party

Add a space and comma between each one, and leave off the space and comma at the end.

Thank you so much !