Assume you are in a flight(air plane). When the flight goes down one side, how do say that? I mean the slide/descend. I feel both are wrong word. What is the correct word? Can I say, "The flight slide on the left side" or simply "The flight slides"?
Airplanes can "roll" to the left or right. This is actually a technical term used for aircraft ("pitch" and "yaw" are the other ways an airplane can be rotate during flight), but it would be understood even outside technical contexts.
Rolling implies that one wing or the other drops relative to the body of the plane. It doesn't explicitly mean that the plane is turning (changing its direction of travel), although that might usually be the case. Ships can also roll. Buses might roll slightly, but normally if we say a bus "rolled" it means it went all the way over on its side. Houses don't normally roll.
A more general word is "tilt". Pretty much anything can "tilt", whether left or right or forwards or backwards. But "tilting" has some connotation that the motion is only slight. You wouldn't normally use "tilt" if the bus went all the way over on its side, for example.
As others mentioned, you can also say an airplane "banks" into a turn. A motorcycle also banks during a turn. But buses don't bank, and houses certainly don't.
Edit Juts to clear up somethign that hasn't been mentioned yet, When something "slides" it means it moves over a surface, with an implication that there's friction between the object and the surface it's resting on. For example if a bus slides, it means either it's wheels are locked preventing it from rolling, or it is moving perpendicular to its normal forward direction. A plane can't slide unless it's on the ground, but it can "slip" sideways when in flight.
Regarding aircraft (this applies to aircraft in general, not just aeroplanes), the word for this is what StoneyB wrote; bank.
Can I say, "The flight slide on the left side" or simply "The flight slides"?
You could say "the aircraft banked left", if it happened in the past. If it is happening now, you could say "the aircraft is banking left".