There could be a number of issues causing a leak on the left side of the vehicle. The question is a bit vague so I'm not sure if you are talking about oil dripping from the vehicle on the floor or an oil stain under the hood or in the wheel well. Oil leaks from the left side dripping on the floor could be engine oil or power steering fluid. Engine oil leaks could literally come from any gasket or seal on the engine and will have to be diagnosed by a qualified technician. Power steering leaks are most common from but not limited to the power steering pump or rack assembly. Oil stains in the engine compartment could be from the engine, power steering, or A/C system. Oil stains on the wheel well could be from a worn strut or a torn axle boot.
It's always important when asking questions or getting your vehicle diagnosed that you be specific as possible and give details when addressing the vehicles problem. This helps the person on the other end (technician or otherwise) key information to help them diagnose the issue or at the very least try to give good feedback to your question.