Placing lines

Hi, I’m a beginner. I want to make accurate drawings for a domestic planning application.
The only way I can see to START a line (or other entity) is by clicking, but how do I accurately start a line at EXACTLY the dimensions I want (rather than just clicking somewhere near)?

What is it that you know that determines where that starting point should be? If you have some way to define that point in space relative to SketchUp’s origin, you can mark that point with a couple of crossing guidelines created with the Tape Measure tool. Or you could draw the line in an arbitray location and then, with the Move tool, move it so that line segment starts at the desired coordinates. After starting the move, type [x,y,z] including the square brackets.

Or does it really matter where that first line is? Typically when I start a model, the very first point is placed at the origin and I work out from there, usually in the positive directions along the solid axis lines.

Many thanks for your prompt reply DaveR. I’ll give it a go & let you know how I get on.