Constraints are automatically applied as you sketch. The constraint symbol on the cursor shows the constraint type. Constraints prevent unwanted changes to a feature when dimensions are changed or referenced geometry is moved.
You can add or edit constraints and dimensions to control sketch shape and size. Before you add constraints , study your sketch to decide which are needed. In a 2D sketch, display the Degrees of Freedom glyphs to determine which geometry is unconstrained, partially constrained, or fully constrained.