Separate tests in groovy

I want separate some maven tests in groovy and i have this syntax:

stash includes: 'Tests/**', name: "tests"
stash includes: 'p2/blabla/site/**', name: "extensions_p2"
stash includes: 'Maven/blavlavla/**', name: "extensions_maven"

I'm at the beging with this programing language and i dont understande it very well...

Those are the test in mave to separete in groovy

<id>machine</id>
<modules>
    <module>../test1</module>
    <module>../test2</module>
    <module>../test3</module>
</modules>  

And what does that mean stash/unstash ?

Please some advices