You must have a valid travel product loaded on your OV-chipkaart when you travel. This might be a season ticket, an e-purse with a balance loaded, and so on. Click travel products for an overview of all travel products and locations where you can buy these.
The ov-chipkaart.nl website has a step-by-step explanation of how to travel using an OV-chipkaart.
The website “Steffie legt de OV-chipkaart uit” provides a straightforward description (in Dutch) of the OV-chipkaart and everything about it. The text is read out loud to you. This website also allows you to “practice” using the different OV-chipkaart machines.