Recess scribe is a way of trimming vinyl seams. One side is trimmed clean and straight with a straight edge. Both sides are then glued in place with the second sheet overlapping the accurate one you had previously trimmed. A recess scribe is then inserted under the top sheet and it sort of hooks against the lower sheet. You then pull the scribe along the entire length of the seam. The under side of the scribe follows the trimmed edge, and as you do this, the top side of the scribe makes a tiny scratch on the top sheet, exactly above the bottom sheet's edge.
Next, you trim the top sheet following that tiny scratch as your guide. You are trimming off the excess overlapped material.
If you did it just right, once the excess piece is moved out of the way, the top sheet should drop down and fit perfectly against the bottom sheet. You use a small steel roller to actually roll and force the top and bottom sheets together. If you get it just right you can sometimes hear it fain't crackle as the pieces sort of snap together.
You don't want it tight and you done't want it loose.
...and the floor is glued and rolled before you do this, so it had better work.