Hi there, Serena, and welcome to planDisney! What a fantastic way to celebrate your son's 18th birthday!
To enter
Star Wars: Galaxy's Edge, you'll first need
theme park tickets and a
theme park reservation for Disneyland Park, which is where you'll find this land.
You'll build your lightsaber at
Savi's Workshop, and my recommendation would be to book your experience before you arrive at the parks. You can do this up to about 45 days out or so - it doesn't look like your arrival date is open for bookings, yet, but I'd keep checking over the next couple weeks.
You can reserve a time on the
Savi's Workshop page or through the
Disneyland mobile app. If you're on the webpage, you'll click the blue button that says "Check Availability," select your date(s), the number of builders (how many lightsabers you'll be building), then select your time. It's a similar process on the mobile app, but to get to the Savi's Workshop page, you'll select the map pin icon, then tap the dropdown list in the top-center of your screen (it will probably say "Attractions" by default) and select "Shops," then scroll through the list and tap Savi's Workshop. From here, you can follow the same steps as the webpage.
Since you'll be celebrating your son's birthday, make sure to also grab a free birthday pin from
Town Hall on Main Street, U.S.A., and maybe even pick up a
Cold Brew Black Caf (my favorite drink!) from
Docking Bay 7 Food and Cargo.
Thank you again for your question, Serena! I hope you all have such a great time visiting the Happiest Place on Earth. Please feel free to come back and see us if you think of any other follow-ups we can help with!
Have a Magical Day,
Greg