Challenge 1: Translate the Terms — Possible Solution
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(a) Table       -> Collection
(b) Row         -> Document
(c) Primary Key -> _id (the field MongoDB uses to uniquely identify
                   every document, generated automatically as an
                   ObjectId if you don't supply your own value)
(d) Column      -> Field

WHY THIS WORKS AS AN ANSWER
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Each MongoDB term plays the exact structural role its relational
counterpart plays, just applied to a document instead of a row: a
collection groups many documents the way a table groups many rows; a
document holds the data for one "thing" the way a row does; a field
holds one named piece of data within that thing the way a column
does; and _id serves the same uniqueness-guaranteeing purpose a
primary key does, just without requiring you to define it yourself.