With the implementation of "Obamacare" everyone has an opportunity to enroll in a new Plan each year with no underwriting (they have to take you and they have to pay for you)
The Most important thing you should know is that if you have any doubt that you do not qualify for subsidies you SHOULD enroll either using the Federal or your State Insurance exchange.
The reason is simple - if you qualify for some subsidy and you do not make your purchase through an exchange you won't get any subsidy. You can either take the subsidy in part or in full - if you don't take all of the subsidy you will get a refundable tax credit when you file your taxes. Again if you do not purchase through an exchange you CANNOT get the subsidy or refundable tax credit.