A strong first step is to do controlled test shooting with the camera in Manual exposure mode and the flash in Manual power. That makes cause-and-effect easier to see than TTL at first.

Use a fixed subject (a mannequin or other still object works well). Keep ISO, aperture, shutter speed, and subject position constant, then change one thing at a time:

• move the flash left to right
• raise/lower the flash
• move it closer/farther
• step through flash power levels from low power up to full

Take notes for each frame; EXIF will record camera settings. Comparing the images to your notes will quickly show how flash position, distance, and power affect the result.

It’s also useful to test how camera modes change flash behavior. On many cameras, A and S often behave more like fill-flash modes, while P and especially M can behave very differently in low light. Learning this early prevents surprises.

For study material, the Strobist Lighting 101 series is a widely recommended starting point. Nikon CLS guides and Neil van Niekerk’s books on on-camera and off-camera flash are also good next steps.