If you are looking at setting up a vendor invoice process then workflow might be something you can look at to help co-ordinate a process. There are a lot of different decisions that you could encode in the workflow to define your process. But before you get to the advanced part you might want to go through the basics of where it is all setup and how it works.
There is a quick overview.
AX7 Build 7.0.4230.16130
Now in this video there is one user involved but the benefit of workflow is allowing it to co-ordinate between the different people in the organization. You can see some other related posts that go into some more details. Some of these will be AX2012 but the major concepts still apply to AX7/Dynamics 365