As a student you can work throughout the academic year. There are, however, different rules for the employment if you are a National of the European Economic Area (EEA) or not. A work permit is required depending on your nationality. Bear in mind that studying must always be the main occupation of someone who works as a student employee.
And what about those 475 hours almost every employer is referring to?
In general you must be employed with a student employment contract.
If you work without a contract, this is often a job as a self-employed person. Be aware that this involves many hidden costs and complicated formalities.