You can specify relative distances by using the command line.
When you are asked for the next point e.g. for a line, enter @3,10 at the command line (Ctrl-M or BLANK to activate).
This will draw the line from the last point e.g. 100,100 to 103,110.
The reference for the @ coordinates is the relative zero, which normally is the point of your last drawing action (little red crossed circle).
The relative zero could be set manually in the Snap menu. It can also be locked, if it is undesired to follow the drawing actions.