What is it you would like to understand? There is just so much. If you're a podcast person, you could listen to Multiamory from the beginning. If you're a reader, then here's some links
https://polyamory.com/threads/most-commonly-cited-advice-articles-master-thread.155304/
If you want to be a good poly partner to this new fella because he already has another partner, then respect the time he spends with his other person/people, and don't expect your relationship to follow the traditional escalation steps. Ask for what you need and want, and if he can't give it, walk away rather than suffering and in turn making him and possibly his other partners suffer your dissatisfaction.
Be prepared for compromise. Be prepared for emergencies leading to cancelled plans. Be prepared to process your emotions around envy (FOMO) and jealousy (fear of loss). Be prepared to be a strong, independent person who can doesn't need the constant attention of a partner to feel secure, happy and fulfilled. Understand your attachment issues, most of us have some form of childhood influence upon them. Be prepared to work on yourself and continue to grow into your own confidence. Those would go for being in a monogamous relationship, too.
As you've already done, be prepared to walk away if something feels hinky. Walking away from unhealthy situations is an act of self-love. Walk away whenever you need to. Some relationship have the ability to be communicated about and improved, some don't. It may take practice to spot the difference. Don't be too hard on yourself if you stay a little long sometimes.
Keep dating other people - don't let this fella control who you can see. He's poly right? Well, what's good for the goose is good for the gander. Don't let him demand monogamy from you. Offer it if you wish, in time, but don't just straight into being with just him. I'm poly because I believe there are always more soulmates out there - the world is huge. Polyamory lets me get to know people as deeply as I wish. I keep some people in my life, and they keep me in theirs, and those connections turn into relationships. Most don't. Be picky.