Monica, just so you know - you have to buy an endless hoop for your machine - to be able to use the endless hoop designs as they were intended to be used, one design after the other along the material - say at the bottom of a pretty little dress or the top of a sheet.
I have one also and you can use any border designs with it. It is great to use to do the top of sheets, borders for quilts, etc. Once you know how to do the marks to match the next section of design to mbroider, it is very easy to use.
Bikermom explained already. I have one on my D1 machine and it is quite easy to use and super results.
'endless' usually means that the top part of the hoop lifts up so you can slide your fabric up then put the hoop back down and keep stitching an endless design - usually for borders, hems etc.