Hi Rozens, there are a couple of different methods.
One option is to enter relative coordinates directly, you do this with an "rx,y" type notation.
For example, start drawing a line. Place the first point somewhere. Now type in "r3,4" and push enter. As you type you will see your text input go into the x,y,z coordinate input in the bottom toolbar. This will place the second point of the line relative to the first point shifted in 3 units in x and 4 units in y.
Another thing that is related is distance constraint. You can activate this by typing a number into the "d" box on the bottom toolbar, or you can also just type a single number into the x,y,z box as well.
So for example, start drawing a line and place the first point somewhere. Now type in "5" and push enter  now the second point that you pick will be constrained to be 5 units away from the first but you can control which direction it is going in. Actually, I think this is the one that matches what you are asking for.
If you want to place the first point of a line relative to some other point, you basically use the same procedure as above, but do it with a construction line. This can be a little tricky because you have to enter the distance constraint before you release the mouse button which finishes the construction line. (Hmmm, looks like there is a little bug here where activating distance constraint when you are doing a construction line also activates it for the actual drawing command as well, I will fix that up).
Let me know if you would like more details on this.
 Michael
