Find your electrical panel. It's usually in a hallway, garage, utility room, or basement. Open the door. Look for the breaker that's in the middle position — not fully ON, not fully OFF, but somewhere in between. That's the tripped one.
Before you reset it, unplug some of the devices on that circuit. Tripped breakers are almost always caused by too many things drawing power at once — a space heater, a hair dryer, and a gaming PC on the same circuit, for example. Or, if you're a homelab person, a server plus a 3D printer plus a laser cutter on one 15A circuit. Ask me how I know.
To reset: push the breaker firmly to the OFF position first (you'll feel it click past center), then push it to ON. You should feel and hear a solid click. If it trips again immediately, there's a short circuit or the breaker itself is failing. Stop at that point. Call a licensed electrician. Don't keep resetting it — you're just damaging the breaker further and potentially starting a fire.
If the breaker resets and holds but trips every time you use a specific appliance, that appliance is the problem — either it's drawing too much current or it has an internal short. Test it on a different circuit in another room. If it trips that circuit too, the appliance needs to be repaired or replaced.
For anything beyond this — adding a circuit for your rack, upgrading your panel, troubleshooting recurring trips — call an electrician. Home electrical is one of those things where the cost of doing it yourself wrong is a house fire. I happily pay pros for that.