How do I write off school expenses, and what does that do?

[xmasbaby0]

What school expenses are you asking about?  You do not "write off" education expenses, but there are some education credits for higher education (above high school level).

https://ttlc.intuit.com/questions/1901172-what-are-education-tax-credits

https://ttlc.intuit.com/questions/1901172-what-education-tax-credits-are-available      

https://www.irs.gov/help/ita/am-i-eligible-to-claim-an-education-credit

https://ttlc.intuit.com/questions/3383321-why-didn-t-i-get-a-credit-or-deduction-for-education-expen...

EDUCATION EXPENSES

Education expenses for grades K-12 are not deductible on your Federal return, whether for private, public, or home schooling, nor are the expenses for tutoring, after school lessons or after school activities, such as dance lessons, sports, etc.  Some states allow deductions/credits for K-12 education and/or home schooling expenses; if your state has these deductions available, you will be prompted to enter them when you prepare your state return.  (As far as I know, the states that offer any sort of K-12 deductions/credits are Arizona,  Illinois, Indiana, Iowa,Louisiana, Minnesota, and Wisconsin)

[Hal_Al]

If you are a dependent, on someone else's (e.g. your parent) return, that person claim the education credut for your college expenses, not you.

Even if you are not a dependent, there are restrictions. A full time unmarried student, under age 24, is only eligible for the refundable portion of the American Opportunity Credit if he supports himself by working. You cannot be supporting yourself on parental support, 529 plans or student loans & grants. You usually must have actually paid tuition, not had it paid by scholarships & grants.  It is usually best if the parent claims that credit. 

If you are a student, over age 23, and are not claimed as a dependent by someone else you may be eligible for the up to $1000 refundable American Opportunity (tuition) Credit. That credit is not dependent on having either kids or earned income. You must be at least a half time undergraduate student. There's even a loop hole available to claim the credit, if you are on scholarship.