You're Ops 15 or higher and just got hit for the first time, or you're about to be -- Station Combat unlocks at Ops 15, letting other players attack your station and vice versa. Everything below is about the two systems the game gives you to control when your station is actually vulnerable: Peace Shields, which you activate, and Ceasefire, which activates itself around maintenance.
The first time your station is attacked, a free 10-minute Peace Shield activates automatically, and this free trigger only fires once every two hours -- if several players attack you inside that window, only the very first attack triggers it. Treat that 10 minutes as a warning window, not real protection: it exists to give you time to activate a longer shield yourself, not to end the threat.
Tap the Shield icon on the right side of the Galaxy view, or open Items > Other and select a Peace Shield from your inventory -- they come in several lengths (1 Hour, 2 Hour, 4 Hour, 8 Hour, 12 Hour, 1 Day, 30 Day). While a Peace Shield is active you cannot attack other players either, so treat it as a full pause on PvP in both directions, not a one-way defense. Shields don't stack: activating a new one overwrites your current one, and it only extends your protection if the new shield is the longer of the two -- activating a shorter shield over a longer one wastes it.
Ceasefire is a separate, automatic protection that activates after scheduled downtime specifically to stop players who log back in faster from raiding everyone else's stations. It only protects your station, not your ships sitting outside it, so a ship caught mining or roaming during Ceasefire is still a normal target. Attacking another player's ship or a ship parked on a mine strips your own Ceasefire protection immediately, with a warning popup first -- and if both you and your target are still under Ceasefire, Station Combat between you simply can't happen at all. Peace Shields and Ceasefire don't interfere with each other: both can be active on your station at once, each with its own expiry timer shown in the HUD.
Station Combat is fought using your Defense Platforms plus whatever combat-ready ships are docked at your station -- ships that are away, upgrading, or under repair take no part in your defense, so a fleet that's all out mining or hunting hostiles leaves your station defended by Platforms alone. If your station is destroyed in the fight, the attacker loots a portion of your stored resources, though your Resource Vault (an upgradable station building) shields part of that from being taken. After the first attack you land, your station automatically gets the free 10-minute shield described above -- so the practical loop for a new player is: get hit once, use the free window to decide whether to buy time with a paid Peace Shield, then come back to actually defend once your ships are home.