Companies registered in Delaware must maintain a registered agent, who will notify the business of any required filings and tax due. For my internet based startup for example, I got a letter notifying me of tax and annual filing due before March 1, 2016 and March 1st of each year. This is the annual required filing and Delaware franchise tax.
The annual report can be filed online. A fixed fee $25-$50 dollars will be accessed in addition to tax due - ranging $75-$165 million depends on the revenue, company type and share structure.
Usually the government also charges a filing fee along with the tax due.
Disclaimer: always check internet information against government websites, and only trust information posted on government tax agency websites. Only certified CPA of the state can give accurate advice. Please only consider this blog post notes of my own personal research NOT as legal or accounting advice.