If you're not, you'll have to buy Office out of pocket. Once you graduate from your current school, Microsoft may check up on you to see if you're still eligible. It's worth noting that this isn't a lifetime gift. If you're eligible, you should receive a code for Office 365, which you can use right away.
To check if you're eligible, head to the official Office 365 Education page and enter your school email address into the box.
However, it's worth giving it a shot to see if you can get Office for free. Not all students can claim this offer, as your institute needs to enroll with Microsoft to benefit from this plan.
If you're wincing at Microsoft Office's price because you're a student, you may be entitled to Office 365 for free.