When sketching and editing there are a number of Display and Drawing settings that can help with the sizing and accuracy of your design.
The Show dimensions shows a temporary dimension as you sketch so you have feedback on the size of your sketch. As strokes intersect we only show the dimensions between these intersections:
The Show guides will display some editing guides during editing. These guides also show when you are creating 90 degree corners, even when the edges are not horizontal or vertical.
If Snap to orthogonals is selected as well then all items in the view will provide horizontal and vertical guidelines allow you to snap and/or align points when editing or when dragging/rotating items.