It gets mixed with air just before going into the engine, once it's mixed with air and is no longer a liquid, it's pretty flammable.. at a certain time a sparkplug creates a spark that sets off the burning (about the highest point in the pistons motion so the expanding flames help push the piston down with extra force, enough to rotate a shaft attached to the tires)

The thing mixing the liquid with air is called a carburetor, there's plenty of videos about them on YouTube for free, a channel called smarter every day did a whole deep dive and built a clear one that he shows working up close and in slow motion and I think it'd answer all questions about them