A telemark binding secures only the toe of your boot, leaving your heel completely free to lift off the ski. This design is what makes the classic telemark turn possible—that distinctive lunging, free-heel style where you drop your back knee as you carve. It's a completely different technique from alpine skiing and requires dedicated practice to learn.
Telemark bindings come in two main interface types: the traditional 75mm (often called 'duckbill') and the newer NTN (New Telemark Norm), which offers better lateral control and releasability. You'll need boots specifically built for whichever system you choose—your regular alpine boots won't work with these.
Telemark bindings are not a substitute for alpine bindings at the resort. They're designed specifically for skiers who want to embrace the free-heel telemark style. If that technique doesn't appeal to you, look at alpine or hybrid bindings instead.