A word about Odoo product versions
At the time of writing, Odoo's latest stable version is version 10, marked on GitHub as branch 10.0. This is the version we will work with throughout the book.
Note
It's important to note that Odoo databases are incompatible between Odoo major versions. This means that if you run an Odoo 10 server against a database created for a previous major version of Odoo, it won't work.
Non-trivial migration work is needed before a database can be used with a later version of the product.
The same is true for addon modules: as a general rule, an addon module developed for an Odoo major version will not work with other versions. When downloading a community module from the web, make sure it targets the Odoo version you are using.
On the other hand, major releases (9.0, 10.0) are expected to receive frequent updates, but these should be mostly bug fixes. They are assured to be "API stable", meaning model data structures and view element identifiers will remain stable. This is important because it means there will be no risk of custom modules breaking due to incompatible changes in the upstream core modules.
Be warned that the version in the master branch will result in the next major stable version, but until then, it's not "API stable" and you should not use it to build custom modules. Doing so is like moving on quicksand: you can't be sure when some changes will be introduced that will break your custom module.
