My MacBook Pro turns on but the screen is black

There are several different variants of that model. Most have Dual graphics. they have an Integrated Intel 4000 GPU built into the processor for "ordinary" graphics tasks and a Discrete Graphics processor with its own display RAM that is used for more demanding graphics or External displays. Macos switches back and forth as it runs.

After a cold start, and before you launch any demanding tasks or third-party browsers, the Integrated Graphics processor should be running. Once you launch creative software, or Chrome, or attach an external display, the Discrete graphics processor will be used.

The first thing to try is to check for a backlight failure, by shining a bright light at the display, to see if stuff is there, just not lit up.

Next, do an SMC reset. then try the simplest thing your Mac can do: Restart with the Option key held to run Startup Manager, whose code is all in ROM, and it needs nothing off the disk. If this does not display anything at all, your Mac needs a hardware evaluation.

There are over 100 different models that carry the name MacBook Pro, issued from 2006 to the present. Their internal architecture varies considerably, and the significance of a black screen varies by model.

Which model is yours, by year, early mid late, screen size and processor speed?