There's a lot to do before launching a new website. It's important to set up a domain name, hosting, analytics, and prepare on-page SEO. The website should also be responsive on different devices, accessible to all users, and fast. In the development world this pre-launch stage is jokingly called the second 90%.
Thankfully, there are some great checklists to simplify this process:
Humaan Checklist — A useful, wide-ranging checklist that also includes items for post-launch.
Process Street Checklist — A high-level checklist with design, marketing, and development items.
I hope this saves you some trouble getting your new website online. Good luck!