I got the below while updating the records in parallel jobs

When I checked the about the error, they say.

The "enq: TX - row lock contention" event often indicates an application level locking problem. The TX enqueue is the transaction enqueue (a.k.a. enq: TX - contention) and can also be related to buffer busy waits, in conditions where multiple transaction attempt to update the same data blocks. TX enqueue is issued when a transaction makes its first change, and released when the transaction performs a COMMIT or ROLLBACK.

I got confused this statement, in conditions where multiple transaction attempt to update the same data blocks.

In this we cant update the multiple rows in same block? row level locking I can understand, how to handle block level? If i want update the records in same block with parallel jobs, how can i do this?

Please advice.