The Tools toolbar displays a number of options such as creating detected constraints, selecting dimension system and so on.
This toolbar is situated at the bottom right of screen. If you cannot see it properly, you can undock it.
See Using Drawing Tools
See Interactive Drafting User's Guide: Applying Constraints
See Restoring Original Properties/Deleted Elements
See Creating Chained Dimension Systems
See Creating Cumulated Dimension Systems
See Creating Stacked Dimension Systems