A loop is an audio recording (or a section of a recording) that is played repeatedly. Loops are ususally short excerpts of instrumental passages or rythmic patterns that can be used as "building blocks" within the larger arrangements. In our context, a groove is a loop or musical pattern that contains more than one instrument.

Most DAW like Garage Band, Pro-Tools, Stylux RMX or Cubase supports the most common loops formats. Just drag and drop one loop in this programs. Now you have a pattern ready for you song, and you can control its tempo.