MetaDataEditor is the tool that lets you edit metadata.  When you edit the MetaDataEditor task you see a window like the one below.

For each metadata field that you can edit, there are radio buttons to choose one of four options. 

If "No Edit" is selected, that field will be unchanged. 

For each field that has "Fixed Value" selected, you will be prompted immediately after closing this window to set a global value for this field.  Every image dropped onto this action will get that value.  This is useful for values that will be the same for all images.  For example if you would like to put the same text (your name) in the "Copyright Holder" field of all the images, you would set this up as a fixed value.

If "Query Once" is selected, then each time there is a drag and drop event (i.e. you drag one or more photos on this Action) you will be asked once for this value.  That means that if you drag a one hundred images onto this Action, all 100 images will get the value you enter at the single prompt.  If you then drag another 30 images onto this action, you will be prompted again and these 30 images will get the value you enter this time.

If "Query per Image" is selected, then you will be prompted for a value for each and every image.  You can enter a unique value for each image.  This is useful for values that change on a per image basis such as image title or comments.

Depending on what settings you have set above, a query will be constructed in a window like the one below.

The values you enter here will be set in the appropriate images as determined by the options you set.