What I did:
1) Created four custom fields
- Quote generated - two option
- Request approval - two option
- Approved - two option, enabled field security
- Approved By - Lookup to User entity
3) Added Approved and Approved By fields to the Opportunity form in a new section called "Approvers Only."
5) Created two Field Security Profiles, one for the Approver of the Opportunity and the other for an everyday end user to allow/not allow update of the Approved field.
6) Created two real-time workflows
- Email sent to the Approver when someone requests for approval
- Email sent to the Opportunity Owner when the Approver approves the Opportunity
Please note that this is a simple approval process. In the scenario where there is multiple approvers required or different iterations of approval is required, consult with your IT partner as they will need to understand the process in order to come up with a more suitable solution.
Relevant blogs about CRM 2013 real time workflows
http://garethtuckercrm.com/2013/12/06/crm-2013-new-features-using-real-time-workflow-for-validation-rules/
In the vlog I mentioned I'd provide a link to Gareth Tucker's blog that explains a bit about real time workflows, so here you go.
http://msdynamicscrmblog.wordpress.com/2013/11/21/workflow-processes-in-dynamics-crm-2013/
Another great piece that explains workflows in CRM 2013. I still don't know who the awesome author is of this blog but it's another good blog to check out.
Happy reading :)