How does a Student Visa works?

I have a student visa valid until October. But my school ends on July. It means I have extra 3 months after the graduation. Does that mean I have to leave Japan after graduation? Can I still apply for working visa within the extra 3 months? We talked to a lawyer and told us we can still apply for change status until October. I'm not quite sure of it since I have read different answers from the previous questions posted in here. Thanks in advance.

Instead of going to a layer you need to inform immigration when your study finished. Than immigration will give you a time. It will be plausible that you can stay till the end of your visa term. Please note that you cannot work any more in the remaining period after your study.

Meanwhile you can try to find a company who is willing to hire you to apply for a work visa. If you do not have a work visa you can change to a tourist visa or you need to return back.