Learning to become an informed citizen usually means having to learn how to read and write English. This is especially true if one is seeking to be admitted to the United States, in which case you will need to demonstrate a basic proficiency in the English language.
There are many types of instruction courses and learning platforms that assist people in learning how to read and write English. These include live instruction, online instruction, learn-by-audio formats and public and private school distance learning. Most require a fee.
A free alternative to a paid course (not directed at passing a citizenship exam) but rather for the person who wants to learn English because they want to increase their proficiency in the language or if they intend on just visiting the United States and want to be able to converse with other english-speaking people, you can do your learning by going on to YouTube. Here you will find many different approaches to learning English for free.