How do ITSM Relationships work, and why would you lock multiple transactions together?

You can relate other transaction types (problem/RfC/KW article), manually (enter ID or search) or automatically (as a follow-up).

You lock multiple transactions together because when many incidents relate to one problem, locking them lets you solve them in order, efficiently. A locked incident/problem/RfC can't be edited unless an admin unlocks it.