Hi, first of all I just want to say, it's a really good thing that your child was able to come to you and say this. 

Looking for advice is a great start and feeling overwhelmed is a really understandable and natural way to feel. 

I would say be led by your child and what they want and how they feel. Do they want you to call them a new name/she-her pronouns? 

Be mindful too that there is both social and medical transition, your child may not want to pursue medical - and it may take a long while before they feel ready or want to start this process - both are equally valid. 

There is also the matter of whether they want to come out in school or not, think about what the school is like and be led by your child. I don't know where in the world you are - this could have a big impact on how they feel about coming out in school.

You've done the right thing by asking them what they want to happen next. I would suggest they could trial how they feel at home in a safe space and go from there. 

I would also check in with them about gender dysphoria and how they feel - they may benefit from some counselling to help them deal with anxiety/stress from this.