Having English as our official language means that official government business at all levels be conducted solely in English. It means the language of record is the English language, and that no one has a right to demand government services in any other language.
This doesn't mean "English Only" it applies to the language of government. People would still use foreign language in everyday life, businesses, and schools.
Official English would also reinforce America's historic message to new immigrants, learning English is a step in assimilation, it encourages immigrants to learn English in order to use government services and participate in the democratic process; it would also define a common language for our nation.