Constraints can be added automatically in AutoCAD, when creating new objects.
Click on the first icon from Status bar to enable the Infer Constraints option.
By right clicking this icon, you can set the options for constraints.
Yet, if you forgot to infer constraints, you can use another option to add automatically these constraints.
Go to Parametric tab and click on the AutoConstrain button, then select the drawing objects you want to be constrained.