  This expository article explains how planar diagrammatics naturally arise in
the study of categorified quantum groups with a focus on the categorification
of quantum sl2. We derive the definition of categorified quantum sl2 and
highlight some of the new structure that arises in categorified quantum groups.
The expert will find a discussion of rescalling isomorphisms for categorified
quantum sl2, a proof that cyclotomic quotients of the nilHecke algebra are
isomorphic to matrix rings over the cohomology ring of Grassmannians, and an
interpretation of `fake bubbles' using symmetric functions.
