If you want clients to be able to self-book, you need to create availabilities. If the time doesn't have an availability on it, it's unavailable.
Step 1: Create Availabilities
Tap your calendar to get started.
Then size the availability box to match the time that you want to be available.
Follow the prompts from there.
Step 2: Check Customer Self-Booking Settings
Here's a video showing how you can customize how clients can self-book you. You can even set it so that they cannot self-book.
Go to "Calendar Settings > Customer Self-Booking" to get started.
After these steps, you're done! Now you just need to share your calendar URL (find it in Online Booking)!