They went from being very large, clumsy, elaborate machines which needed lots of human intervention to one program on a floppy disk. Images on CADD systems are drawn with the aid of a keyboard, mouse, or tracking ball. One selects the starting point of a line, the ending point, and the line is drawn. A scale at the bottom of the screen tells how long the line will be. On some CADD systems, the computer itself can measure how long the line will be while the operator inputs the length of the line.
Lines are the basis of all drawings.
That's what different CADD commands are made for. Different CADD commands make different things on the screen possible. There are commands for dimensioning, labelling, making circles, boxes, etc. This allows the operator to rotate, tip, flip, and move the object by degrees. Top, front, and rear views are used.