The way I like to think about parameters is it’s like a handoff. You need the page link to first send the parameter (I do this by setting up a link element to send to "URL?id=“Something from database”) and then set up the Bubble page on the other side to receive it using a parent group and setting it to “get parameter from URL’s ID”. Parameters are best used when you need to display different data like listings and want to be able to open many different tabs.
For states, I don’t think you can beat this post: How "State of an Element" feature works exactly?