Scarif is a tropical island paradise where the plans for the Death star are being held in the main building. It won't surprise you that the film was filmed in the Seychelles, oh what terrible life it is for actors nowadays.
At the top of the tower, off picture is a satellite dish. From there, Jyn Erso plans to transmit the plans for the Death Star. The planet has been enveloped by a shield meaning ships can't get in or out of the planet. Those on the base and surrounding are doomed unless they could get to safety.
The final battle of Star Wars - Rogue One takes place here. As its a main Imperial base, it has everything you would expect, Stormtroopers and AT-AT Walkers. In addition to the ground battle, there is a space battle.
Jyn, Cassian and K-2SO sneak into the main tower whilst the other rebel fighters create a distraction by launching an attack on the base. The attack alerts Grand Moff Tarkin who orders that the Death Star be moved to the planet so he can destroy the base with the new weapon.
Had Cassian Andor and Jyrn Erso been a bit more sneaky and not announced to everyone that they had arrived, they could well have survived the operation. By shooting the place up, they alerted both the Galactic Empire and the Rebel Alliance that they were they there. When word that the battle was in place, both the Rebel Alliance and the Death Star moved to the planet.