To add your booking page button-link to SquareSpace, you will need to utilize a SquareSpace code block.
To get the code for your own booking button log into Appointlet and click Share in the upper left. From there choose Website.
Now go down to step 5 and copy the code to your clipboard. Here is an animated screenshot to show you the steps:
Paste it into your SquareSpace code block. Save and check out your page to test it out. For more information on how to user the Button block on Squarespace, read this guide.