What's the difference between a burrito and a tortilla?
Depending on where you are, the word tortilla can mean a few different things.  In Mexico it refers to a flatbread made of either wheat or corn and a few other ingredients.  These flatbreads tend to come in standard sizes in the United States at least, one of which might be labeled the "burrito" size.

A burrito is one use for a tortilla.  A burrito consists of a wheat flour tortilla wrapped around a filling.  Often the filling might include beans, cooked meat, rice, and perhaps vegetables.