Can someone PLEASE explain the laws for purchasing marijuana?

To my understanding, using weed recreationally at a private residence IS legal, and you can own up to four plants, but it is also illegal to purchase weed recreationally (without a medical card). Buying the seeds appears to be illegal as well, and of course you can't buy them outside the state and bring them here because that would be a federal crime. Unless I'm mistaken, it sounds like I have to break the law at some point in order to get my hands on weed. I'm confused on why it would be legalized in the first place when nobody is allowed to buy it.