The red BRAKE warning light on your dash is different from the amber ABS light, and when it stays on it deserves attention. It flags issues with the base braking system, not the anti-lock system. Here are the common causes.
The parking brake is engaged
The simplest cause: the parking brake is on, or not fully released. The red brake light comes on whenever the parking brake is applied - so first make sure it is all the way down or off. A parking-brake switch that sticks can also keep the light on; see brake warning lights meaning.
Low brake fluid
A very common cause is low fluid in the reservoir - a float sensor triggers the red light when the level drops. That low level usually means worn pads or a leak - see why is my reservoir low and brake fluid leak signs. Check the fluid before anything else; do not just top it off without finding why.
A hydraulic pressure difference
Many cars have a pressure-differential switch (in the combination valve) that lights the brake warning if one circuit loses pressure versus the other - a sign of a leak or failure in one half of the split system; see when a soft pedal is urgent. This is a serious, stop-and-check cause.
What to do
Check the parking brake, then the fluid level and condition. If both are fine and the light stays on - especially with any change in pedal feel - treat it as a hydraulic fault and get it inspected promptly. Keep the system healthy with fresh fluid, quality pads, and hardware.