Hecarim is a late game offtank jungler capable of attack carrying or AP carrying. Hecarims ability's mainly start at high cooldowns but get decently low later on.

In a 1v1 fight you want to cut through the jungle wait for your opponent to move away from the safety of the turret when they are about equally between your turret and there come out with you E and leap towards them with your ult and knock them back activating your Q as there knocked back then activating your W and attack them and use Q whenever it comes off cooldown.

In a teamfight you want to do relatively the same thing. But instead of cutting behind the other team you want to stay with your allies. To initiate simply leap into the other team with your ult and hit them with everything you have. If they try to focus you activate your Q and W this will give you a shield and damage them.

-Hecarim becomes a very dominant force late game but isnt super strong early game
-Hecarim needs to have large amounts of farm to become succesful
-Hecarim is a commonly banned champion in ranked
-In teamfights your commonly focused so you need to get tank items