When a supplier receives a job through the supplier portal, he can very easily accept or reject this job on the portal, using the corresponding buttons:
However, these buttons are only available if you activated the corresponding option in the supplier portal (Outsourcing tab of the job):
When the supplier clicks on one of these buttons, a pop-up opens where he/she can enter a comment to justify his/her acceptance/rejection, or ask a question.
In the details of the outsourcing, you automatically see if the supplier accepted or rejected the job on the portal, or if you're still waiting on a confirmation from him/her.
If a supplier accepted the job, the status of the outsourcing automatically switches to 'In progress'.
You can also tick the option on the portal to automatically create a PO for the supplier when he accepts the job:
Note: The options to allow a supplier to accept/reject jobs on the portal and to automatically create a PO on acceptance can be activated by default under Settings > Advanced options: