I am a W2 employee paid by 100% commission only. I own my own computer, furniture etc. They only provide the office. How can I deduct my expenses?

as a W2 employee you can't deduct any non-reimbursed expenses 

Sorry---the tax laws that changed for 2018 and beyond say W-2 employees cannot deduct job-related expenses on a federal return.  State laws vary.

https://ttlc.intuit.com/questions/4482873-which-federal-tax-deductions-have-been-suspended-by-tax-reform