I am a W-2 contractor, my company does not offer a 401K plan, how much i contribute pre-tax for retirement?

how can I contribute to a pre-tax retirement plan and how much can i contribute??

The only thing you can do is a Roth IRA, which is still post-tax, but at least you will not pay taxes on any profits or with drawls. You can only pay in $5000 per year unless you are 55+. The pretax is for employer sponsored 401k and 403b plans, I think.