Hi Kasey,
Wanting to be supportive and seeking advice is a great first step. Our Transgender Parent Guide may be helpful and we recommend reading through the resources there. Adjusting to using different pronouns for your son can take time and practice, but it is a way to show him you support him and are trying. If you do his laundry, you could practice while folding laundry by saying, “This is his shirt” or whatever article of clothing it is. It may seem silly, but it’s an easy way to practice using his pronouns and we as humans often learn through repetition.
While it may seem like a fad because of the increase in youth coming out as LGBT, we’ve seen that the reality is that more youth (and adults) are coming out because it feels safer to do so these days. It’s great that he feels safe enough to tell you who he is. Letting him figure himself out, while working on using the pronouns he’s asked you to use would be a good next step to showing you respect and love him.