Use 'join up' to express initiating membership with a new group, often implying active participation.

Group Affiliation

'Join up' originated from military context but can be used for other organized groups.

Militaristic Origins

'Join up' is conversational and might not always fit formal writing or speech.

Used when linking separate elements to form a unified whole.

Often used in instructions for visual tasks, like drawing or crafting.

Can imply forming a path or course of action by linking stages or points.