A Concordance will help you trace a word -- or a word's usage throughout the Bible. You can also find a passage using keywords if you don't remember the location of the whole passage. Concordances help with primary source research as you are viewing a word or passage within its original context.
A Commentary provides context and analysis of words and passages-- through historical, cultural or other areas of scholarship. Commentaries are secondary sources to aid in interpretation of the text.
commentar? and [search term]
It may also be listed as Criticism, Interpretation, etc. as the subject
criticism interpretation [search term]