3D Printer Calibration

I need help calibrating my 3D printer. I'm experiencing issues with prints not sticking well to the build plate, which is a textured flexible plate. The prints usually come loose partway through the print. I bought a glass plate but i don't know how to calibrate it so that the print nozzle does hit the glass. Ender 3printer.

I would also like help connecting Tinkercad and Thingiverse or similar. 10 year old willk mostly be using it.

Ideal skills and experience:
- Expertise in 3D printer calibration
- Familiarity with textured flexible build plates and glass plates
- Problem-solving skills to diagnose and fix adhesion issues