Pay with check online?

Well, to put it simply, I’m supposed to buy a certain amount of music supplies for my school’s music club, but the money I have is in the form of a check, addressed to the vendor I plan on buying for.

The only catch is, it’s an online site, and I don’t see much about paying with a check on the site, so I’m a bit confused.

Perhaps I’m being completely obtuse, but does anyone have any suggestions about what to do here?