A car pulling to one side is almost always one of three things: uneven tyre pressures, wheel alignment that's drifted out, or a brake caliper sticking on one side. The first two are quick fixes. A sticking caliper needs proper attention — it makes the wheel hot and chews brake pads on one side.
Start with tyre pressures — the right values are on the inside of the driver's door. If pressures are even and it still pulls, alignment is the next suspect, especially if you've recently hit a kerb or pothole.
If the pull only shows up when braking (not just cruising), that points at the brakes — a stuck caliper, a glazed pad or a collapsed brake hose. Don't ignore that one: braking imbalance gets dangerous fast.