A Parallel Block is started at a Parallel (AND) Split and ended at a Parallel (AND) Join (the 'brackets'). It indicates that, of the possible paths within the block, many or all can be followed.
The split has several transitions outbound from it, indicating the possible paths that a process instance could follow. Since this is a Parallel block, any number of the paths can be followed in parallel (assuming their transition conditions are met).
The Parallel Split must be matched by a corresponding Parallel Join. This indicates the point at which all the parallel paths must be synchronized before the workflow can continue.