5.6.0+
If you have selected an OGC Layer in Studio you will notice that there is a Metadata button. If you click this the Layer Metadata Editor will be displayed.
This is where you may enter an Abstract to populate the ows_abstract and a list of Keywords to populate the ows_keyword_list in the .MAP file.
Abstract
Simply type the wording in the box provided.
Keywords
Enter a Keyword and then click on the green plus 
to add it to the list. Repeat with any other Keyword. You can remove a Keyword from the list by first selecting it and then clicking the red cross 
or re-order the list by selecting a keyword and then using the up 
and down 
arrows accordingly.
When you are happy click OK or click Cancel to return without updating the metadata for the Layer.
Now if you look a the auto generated .map file you will see your entries e.g.
