In HBook > Misc, you will find a setting to display Terms and Conditions section. Once you have set that setting to "Yes", you can customize the text displayed for that checkbox in HBook > Text > Book now area.
If you wish to add a link to your terms and conditions page, it will look like this, for example:
I have read and I accept the <a href="mysite.com/terms-and-condition-url" target="_blank">terms and conditions</a> for this booking.