When an invoice is submitted for approval, the invoice looks at the criteria of each approval channel. If the invoice matches an approval channel, it will go to the approvers in the channel. This means that one invoice can go to multiple approval channels as long as it matches its criteria.
The approval channels also have a sequence. An invoice will follow the sequence and go to the approvers set out in the approval channel.
If you have stop channels set up, then once an invoice matches a stop channel's criteria, it will not continue to the rest of the approval channels.