When you receive an offer from an institution and decide to accept the offer, you are required to make a deposit payment to the institution in most cases. This deposit indicates your commitment towards the offer.
Once the deposit payment is received, the institution will proceed to reserve a place for you, and grant you a confirmation document that will allow you to apply for your student visa. The deposit is usually non-refundable (unless your visa application is unsuccessful). The deposit will eventually offset your tuition fees, and in some cases, your health insurance as well.