There are quite a few different types of web-based map service that can be loaded in QGIS. Each type of web service provides data; often, this is the same data in different ways. This recipe is about helping you figure out what type of web service you want to consume, and conversely what type of web service you may want to create for others to use.
This recipe is all about thinking, so you don't need anything in particular to start. It does help if you have a project in mind and some type of data you are interested in using or creating. Most, if not all, of these methods require an Internet connection or a local server, providing these services. Of course, if you have the data locally, you should probably just load it directly.
To help with the following section, here's a list of acronyms: