Maven has a life cycle in its build process. The key concept is "Phase". Do not be confused by another concept "goal". There are different but related. For example, "package" is a phase. It is not a goal.
Maven can support a number of different life cycles. But the mostly used one is the default Maven life cycle.
The default life cycle has the following phases (For a more detailed description, see reference). And they are stepped through in order until it reaches at the phase that is specified in the Maven command.
Maven delegates the work to Maven plugins.
Plugin goals can be attached to a life cycle phase. When Maven moves through the phases, it executes the goals attached to each phase. Each phase can have zero or more goals bound to it.
A phase may mean different things to different projects. For example, for the package phase, a JAR project will produce a JAR file, while a web application will produce a WAR file.
If no plugin is specified in the pom file, Maven seems to use its default plugins. See reference.
You can run Maven by specifying a phase as in "mvn install". You can also run Maven by specifying the actual goals as in "mvn resources:resources compiler:compile".