Copy the button code and paste it on your site
The code creates a "Book an appointment" button in your own colour that goes to your booking page.
Copy the code
Go to Settings, Your booking link. Under "On your own website (for your web developer)" click "Copy code".
Paste it on your site
WordPress: a "Custom HTML" block. Wix: "Embed code". Squarespace: a "Code" block. Other sites: wherever you can paste HTML.
Change the text (optional)
Add data-tekst="Book now" to the code for different button text.
Rather not use code? A plain link or button to your booking link works just as well.