Employment is your occupation or the fact that you have a job. If you are looking for employment, you might start by attending a job fair — if you make a good impression, you might get hired immediately.
If you have employment, it means you have a job. You can also use the noun employment to talk about exactly what that job involves, like your employment in the entertainment industry or in the carnival business. Employment also refers to the act of giving someone a job. The Latin root is the word implicare, meaning "enfold, involve, or be connected with."