Its to bad the guy at the flyshop didn't take the time to explain it all to you as he should have.

What kind of waters are you fishing, lakes, rivers , small streams, Ocean ?
what type of fishing, Bass, Gills, Trout, Steelhead, Salmon etc.

Everybodys opinion varies on the subject of leaders and tippets and even on what knot you should tie them on with.