Number of processes defines how many processes each queue will start. For instance, if you have 2 processes assigned for a particular queue, there will be 2 processes in the database for that particular queue and the queue will be able to process 2 jobs simultaneously. 

However, you should not increase the number of processes given for queues as it could have adverse effects. Changing the number of processes should be done after doing some diligent analysis first, especially for the default queue. This is because…

1. Some jobs may need to be run isolated from others. 
2. Some jobs may need to be run in a particular order.
3. Some may take a long time to run which could block other jobs in the quueue.
4. If you run certain jobs in parallel, they could create deadlocks in the database.

Above facts should be taken into account when changing the number of processes assigned for queues. 

Furthermore, you need to have enough job_queue_processes in the database to facilitate the total number of processes you have assigned for the queues. You can check the value assigned for job_queue_processes parameter in the database for this. Number of job_queue_processes should usually be "the sum of processes assigned for each queue” + “5 more processes for Oracle internal jobs”.

Hope this answers your question.