Calibrate your drawings to begin takeoff, byusing the Calibrate Tool(On the right hand side) and single click on a point and double click on the end point.
During the Takeoff process you may need to create sets for categories (eg. Foundations, Electrical etc.) that may have different requirements (eg. dimensions, material etc.)
If your project has provisional amounts you can specify which categories (eg. Electrical) they apply to as well as specify points/measurements. (Note: To add values to your provisional amounts you need to visit the Estimating tab)