The deductible is the amount that you are responsible to pay before the insurance benefits start paying for the treatments or services.
If you choose a zero ($0) deductible, that means you are not required to pay any deductible and your benefits start immediately. If a plan pays 80% for the first $5,000, and 100% after that, this means that the insurance pays 80% for your first bills of up to $5,000.