I am developing an application and would like to add a custom modal window, similar to the attached images, to be displayed to the client during the installation process. Could you please guide me on how to implement this in HubSpot?
If you're looking to add a modal via a CRM extension checkout this documentation. But based on your 3 screen shots, 2 of which contain modals and all of them containing tool tips I think you may be referring to a tooltip onboarding experience like introjs.com. If that is the case, unfortunately outside of a browser extension there is not yet a method to extend the CRM UI in this way.