How do I heal in Minecraft Beta 1.8?

Solution 1:

here is the article on the minecraft wiki on Food and Health

As of 1.8, health is not restored by consuming food, but rather slowly regenerates when the player's "Food Bar" is full.

and here

In the 1.8 update, the food mechanic was changed-- No longer does eating food regain health, but instead fills the Hunger Meter, which goes down when the player does things like running, sprinting, and mining. When the player has 9 or more meat bones on the hunger meter, their health will slowly regenerate.

Solution 2:

You (should) auto regen health when your food bar is full. Food no longer directly heals you.