You need to have a local testing environment of some sort running a webserver of some kind with php and mysql installed. Then you use the “Open url” option on the start page and enter the local website address.
This also works for External websites hosted out there on the internet. You will not be able to save changes to external websites directly via the internet with Pinegrow. You will be able to save files locally on your computer. This works well for local testing environments.
Think of Pinegrow as the front end Pretty tool. The backend database management and actual programming you should use a programming IDE or something like Notpad++, Atom, Brackets, Visual Studio Code or similar tools.
You are not going to find a one stop shop solution that works reliably or produces standards compliant code. Choose the right tool for the job. Pinegrow is for the front end Pretty, AFTER you have the content management whether static files or database based setup and working.