So your child has come out to you. What do you do now?

You support them. Nothing has changed about them, they’re getting to live more openly. They may however start being victimised by others and will need your care and support.
You believe them. Kids are prone to phases, sure. Its how they grow, and learn, and find their identity. If you don’t believe or support them now, it tells them you don’t take them seriously, and they’ll have trouble trusting you in future.
You thank them. They likely agonised over telling you or not – how many stories are there of LGBTQIA people losing their families when they come out? This is a brave, risky moment for your child. Thank them for letting you know who they really are.
You be open to learning. Especially if you’re not really up to date on how things are for your child’s identity. You may have a lot of learning to do. Be open to it, it’ll be worth the world to them. Learning their language – a new name, pronoun and other terms may come along with this. You may have to unlearn old terms that you may have used, that you may now be told are hurtful.
You seek community resources. There’s fantastic resources out there to help parents of LGBTQIA children be supportive allies. PFLAG is a fantastic place to start!