1. To form or get into a line along some orienting shape, mark, perimeter, etc. We all lined up along the edge of the pool, waiting for the instructor's signal to dive in. Please line up along the dotted line I've marked for you on the stage.

2. To cause or direct someone or something to form or get into a line along some orienting shape, mark, perimeter, etc. In this usage, a noun or pronoun can be used before or after "up." The coach lined us up along the sidelines and then made us run sprints for the rest of practice. We'll need to line up these lights along the border of the footpath so people don't accidentally walk on the lawn during the night.

3. To cause or direct someone or something to form or get into a row atop something. In this usage, a noun or pronoun can be used before or after "up." The drill instructor lined the trainees up along the wall and told them to jump at the same time. We lined up photos of our wedding day along the mantelpiece.