Line pins are nearly always used in conjunction with a brick line and line blocks.
Line blocks
Line blocks are small, roughly “L” shaped blocks typically made from plastic, wood or metal. They are use to secure a brick line to a course of bricks so that you can ensure that, as the wall is built higher, it stays level and true. Line pins are most often used as a starting point anchor – they are used in conjunction with a line block when you need to take a brick line around a 90-degree angle.
Brick line
A brick line is essentially a piece of string typically made from nylon. The line is used to create a reference guide to aid you in the laying of bricks in a level course.