What is the difference between contain and content?

"Contain" is a verb which means to keep something in something else. Like, "The hazardous waste was contained in the barrel."

"Content" can be either a noun or an adjective. To speak of content as a noun, it is just what's inside of something. Like, tables of contents means a table of what's inside a book. The contents of a box is what's inside the box. Used this way, it is often plural and the stress is on the first syllable: CON tents.

Content as an adjective means that someone is happy.Used this way, the stress is on the second syllable: con TENT.