Wow! That's a hard question, but there are so similar. They both mean protection/saving.
I think of conservation as the protection of natural things such as land, parks, natural resources, animals etc
I think of preservation as protecting (or saving for later) other sorts of things: pictures, cultures, buildings, food, landmarks, heritage, language, etc
Preserve is more of saving it for later use/enjoyment and Conserve is more of reducing the amount used/impacted.
There's a good chance you'll hear them used wrong/interchangeably often. For example, many people say "I'm conserving my energy." Technically they mean "I'm preserving my energy." But they don't say it the "right" way, but everyone knows what they mean.