First, check whether the display still works. If the picture is clear, touch responds everywhere and there are no colored lines or dark blotches, the damage is probably limited to the glass. That matters, because on many iPhone and Samsung models a working panel can have just the front glass replaced, keeping your original OLED and everything that depends on it, including Face ID and color accuracy.
Second, stop the crack from spreading. Put a screen protector or even clear packing tape over the damage. Glass cracks grow with every pocket, every temperature change and every tap, and a small corner crack can become a web across the display in a day or two. Tape also keeps glass slivers off your finger.
Third, avoid moisture. A cracked screen is no longer sealed, so keep the phone out of the rain, off the bathroom counter and away from the pool until it's repaired. Water that gets under cracked glass is what turns a screen repair into a board repair.
Finally, back it up, then bring it in. Our diagnostic is free, and we'll tell you whether your phone is a candidate for a glass-only repair or needs a full display. Common models are usually done the same day, and you'll have a price before we open anything.