My car swerves or skids at certain times and I don't know how to fix it?

Whenever it hits a bumpy road surface it seems to swerve unsteadily and I have to pull the steering wheel to stop it veering to the right or left. Also when I pull away quickly at a roundabout, the car sometimes skids to the right and left, and if I hit surface water it also skids uncontrollably. Is it wheel alignment or balance or something else, please help?