A good beginner resource is the Strobist website, which has free introductory lessons and practical exercises for learning flash.

For getting started, focus on a few basics:

• If possible, use the flash off-camera for more natural-looking light.
• If you must keep it on-camera, try bouncing it off a white ceiling or wall instead of aiming it straight at the subject.
• If flash is your main light source, manual exposure on the camera is often a good starting point.
• For outdoor fill flash, aperture priority can work well, but watch your shutter speed.

One important limitation: the Sigma EF-500 DG ST is a system-dedicated flash, meaning it’s made for a specific camera brand version. If it matches your camera system, you may get automatic features like TTL-style communication. If it’s for a different brand, you may only get very basic firing behavior, limited power options, no automatic zoom control, or in some cases it may not work properly at all. The ST model is also more basic than higher-end flashes, with fewer manual controls.