OK. Now, that you already know a few things about each role, a natural question arises ...

How and when to use different Wordpress user roles?

That's a tough question, because every website has it's own purpose and you won't find two site owners truly think alike. However, I have a few recommendations for you and hopefully they will help you to make the right choices ...

First of all, a security issue. If you are going to use unsecured networks (airports, shops, etc) to log in, you should create an editor account for yourself which can be used to perform the usual daily content management tasks without exposing your admin account to hacking attempts or any other security issues that might appear in these places.

The contributor role: honestly, in my opinion it's quite useless, but if you are planning to publish a lot of user generated content, it could be a good idea to use a bunch of contributors and a trusted, well-trained editor who can efficiently manage the continuous incoming content flow. Another possible scenario: you might want to "test out" a new user before granting him author privileges.

The author role: if you are planning to accept user generated content, but you are going to work with a smaller team you should simply give them the author role, allowing them to manage their own content without interfering with others.

This probably goes without saying, but I'll say it: using both contributors and authors just doesn't make sense ...

The editor role: the truth is that you don't necessarily need an editor. If you have enough time, you can do the job even if you have a horde of contributors or authors. I admit, it sounds like a real nightmare to me, but it's really up to you to find the right balance ...