The Tax Cuts and Jobs Act ended the individual mandate starting in 2019. So for 2018, you’ll be penalized unless you have minimum essential health coverage or qualify for an exemption from coverage. You can find a list of exemptions in the instructions to Form 8965 (https://www.irs.gov/pub/irs-pdf/i8965.pdf).
Advance payment of current tax liability based either on wage withholdings or installment payments of your estimated tax liability. To avoid penalties, you generally must pay to the IRS either 90% of your final tax liability, or either 100% or 110% of the prior year’s tax liability, depending on your adjusted gross income.