This is a tool to schedule things between groups of people. It runs completely in your browser: all the information is stored in the URL.
To create an event, set your name then select your available times.
Click "Copy link" and send the link to the next person whose times you want to know about. They set their name and availability and on it goes.
This means that everyone can contribute their availability without needing an account.
It also means that you have to keep sending a link to-and-fro whenever you need to make updates, which might be annoying depending on your needs.
If "Alice" already has times set, typing "Alice" into the name field and clicking off the input will make those fields editable.
For cases where you need to make frequent updates, consider using a dedicated scheduling tool or something like Google Sheets.