Why does my Minecraft seem to be lacking things that other players have? I have bought the game, but yet....?

Hey! I bought Minecraft, and I play it a lot (through the browser) on my PC. I have noticed, through watching many youtube videos, that there is a lot I can't do on mine. For instance; I can't do any of the physics stuff, I can't make a mine cart booster, I can't make fishing polls, There is no clay on my map, etc. I'm just wondering why. Is it because I'm playing it in the browser? If someone could help me out, I'd much appreciate it! :) Thanks!!