Engines evaluate a position based on a number of factors - material imbalance, king safety, control of the center, pawn structure etc. My understanding is that they then combine these separate evaluations using a weighting for each (which can be adjusted), to produce a final score for the position.
Is there an engine which can display a breakdown of the separate evaluations?
Material: 0.00 King safety: -1.21 Center control: +0.87
Which means that material is equal, but black's king is less safe than whites, and white has better control of the center.