Hi there. Nature prophet is a great hero, and also my favourite. In this easy guide I show you how to make him usefull and feared.
First of all, you go jungle. You can tank mid-camps with 2 of your treants, especially if you buy basilius in the beginning. Don't bother yourself with ganking and pushing until you get Shadow Blade. Then you can teleport to your creeps, make treants and push the lane. If you see enemies coming for you - just use Shadow Blade, get yourself away from the tower and teleport wherever you want.
Your main goal in the game is to push constantly. Of course you can participate in teamfights, but be carefull - Furion is very squishy. He can be defined as a "glass canon" - dealing high amount of damage in mid and late game, but also having low amount of health and armor.
Good luck and remember - you alone with your base-raping capability can deal a lot of trouble to your enemies, but you need your team to distract them.