Shingles are smooth and are used for roofing or exterior walls.
Shakes are rough (hand split) and used for side walls.
Red Cedar shingles are 24" long and variable width. The top of the shingle is nominally 3/4" thick and tapers to near zero at the bottom of the shingle. The reveal (exposure) is typically 10". There are 5 bundles to a square and a square covers a 10' x 10' area.
Northern White Cedar shakes are hand split with a fairly uniform thickness from top to bottom, nominally 1/2". The length is 16" to 18" with a variable width. The reveal (exposure) is typically 9". There are 10 bundles to a square.
Costs will vary, but the cost per square for Northern White Cedar shakes is nearly twice the Red Cedar shingle cost per square.