Buffs: Food

The slice of cheese next to the minimap indicates a food buff
and shows the time remaining.  If you scroll your cursor over it,
it will tell you what exactly is being buffed.

Some food just heals you once you are out of combat. Other foods not only give you health (and sometimes mana), they also give you a buff to your stats for a period of time.  Most give 2 buffs:  stamina since everyone can use stamina plus one other.  Low level food buffs are for stamina and spirit. The spirit only helps toons that use mana as a resource since spirit speeds up the regeneration of mana. If you don't use mana, it provides no benefit. 

Foods that contain buffs are almost all made using the cooking profession.  At higher levels, foods start to add other buffs that increase useful stats for different toons.  At that point it becomes important to know which ones will give you an advantage and learn to make those foods with your cooking skill.  Or you can buy them in the Auction House, since food is not soulbound.  Food without buffs can be bought at most inns, many vendors, and is dropped by mobs.