string will help you to mark straight lines, define angels and so. To tighten the string one needs a rapid knot, easy to make and to undo.
Step 1: Other tools
a length of string, slightly elastic
something to measure with
and possibly some tongs
Step 2: Measure and mark
Its up to you what you want, where you need the line for, or what angels you want to define. her is just an abstract example
Step 3: Nailing
as long as they hold a little strain, don't hammer them in too far
Step 4: Fix knot 1
On on side just a simple knot will do. you might leave it afterwards
Step 5: The Knot , firts step
the idea is to twist the loop 8 to 12 times, depending much on the string resistance. I mostly twist counterclock wise, doesn't seem to matter much.
Step 6: Tightening
You might want to help the tightening, pulling the fixed part of the string towards the nail, also pulling the loose end , working with both hands.
Step 7: Closing the knot
by moving the loose end, keeping it tight, to the opposite side, the knot moves towards the nail. then let go. if all is correct, the knot stays. If it slips, try again, twisting is a couple of times more
Step 8: Ready
you now have a tight string, a straight line, mark the piece where you need it, or transport the angle to your work piece.
Step 9: Loosening
Bring the loose end again towards te tight string, and pull. The knot is gone. Get the twisted string of the nail.
Step 10: Finished
pull the nails out, roll the string, you can use it for years. String is a basic tool,
try it, the knot is made in seconds.
good luck with your work and projects.