Once you are ready to submit your Bid Response to your customer, you will got to the Publish tab and press Finish on the bottom right.
If you are not ready to publish your Bid Response, you can click Save and come back to it later. You can also amend any of the data before publishing by clicking Previous or simply clicking on the relevant tab.
See the articles below for additional information on Bid Requests:
Joining and Accepting a Bid Request
Bid Request - Confirming Bid has Been Submitted
Submitting Bid Questions & Messages