"Pull" has been used in several posts here. It has different meanings. When you pull a thread, you take out one thread in the cross grain, which will show the exact straight grain line of the width. But then those edges have to match exactly when you fold the fabric in half again (or in quarters).
In order to match this grain line when folded, you need to "pull" the fabric. When the fabric is folded in half, you will find one half is longer than the other. Lay fabric out flat. Grasp the shorter corner with one hand, then grasp the other side of the fabric at the other selvage about 42 inches down from the other corner so that you are pulling at a 45º angle. Give that bias a little tug. Move your hands a few inches closer to the long corner and tug again. Repeat the tugging until you get right to the corner. Now go back to your first tug and move down to the other end of the fabric and work into that corner. Fold the fabric in half again and see if it needs more tugging. You may see that it is perfect now or you may see that you need to tug a lot harder.
In home-ec class, we always pulled a thread and then tugged until the ends were even.