The clothes that you wear to work will vary according to the type of job you do. A City business man, for example, will need to wear completely different clothes to someone who works on a building site.
People who work in office based 'white collar' jobs will tend to wear clothes that are either fairly formal or smart casual depending on the policy of their employer. So, suits or trousers/skirts and a smart jacket may be the norm here. People who spend a lot of time in customer facing roles will need to be smart and well presented and, in many organisations (such as banks and shops) may also have to wear a uniform.
People working in specific roles such as fire fighters, police men and ambulance staff will also wear a uniform as their work clothes. Often these uniforms can be used to denote a job. In a hospital, for example, doctors will generally wear a white coat and nurses will wear different coloured uniforms according to their grades.
People who take on non-office based jobs such as blue collar jobs generally do not need to dress formally. Their work clothes are designed to be practical and to give them protection in the event of accidents. So, for example, someone working on a building site will wear comfortable clothes that will not restrict their work. It won't really matter here how dirty these clothes get. They may also wear other stuff such as hard hats and reinforced boots and shoes to protect their heads and feet.