The ACT is administered by ACT Inc, a non-profit organization that provides educational and workplace resources from elementary school through career. The test is comprised of four required sub-sections: English, Math, Reading, and Science. There is an optional Writing Test (an essay), which is scored separately from the other sections. Some colleges require the Writing Test, so make sure to confirm each college’s admission requirements.

Time: 2 hours 55 min, 3 hours 35 minutes with writing
Cost: $46, $62 with writing
Highest Possible Score: 36

The test is scored out of 36. To calculate the total score, which is called the composite score, the four sub-sections are given a scaled score ranging from 1-36. Then, the average is calculated to form the composite score.
The raw score is the number of questions answered correctly. Incorrect answers do not affect the raw score. To go from raw to scaled score, ACT Inc scales the scores to adjust it based on the variations of tests from different days. You can check out the chart under resources to translate raw and scaled scores.
The Writing Test has its own separate score. Two graders give the essay a score from 1-6, and then the average is calculated. The final score ranges from 2 to 12. Then, the Writing Test grade is combined with the English and Reading grades for a English/Language Arts subscore between 1 and 36. This score does not affect the composite score.
Viewing and sending scores can be done through the ACT Inc website.

Many schools superscore the ACT. This means the colleges will view all ACT scores sent in and take the highest scores from each section, forming the highest-possible composite score. With a policy called Score Choice, you can choose which scores to send and not to send. However, you cannot choose which sections to send to schools. All sections of a test from a certain test day must be set in. Always make sure to research each college’s admission policy to see if they superscore or allow a Score Choice.

Visit the ACT home page to register for a test, look at sample questions, etc.
The ACT Online Prep Program can be purchased for $39.95. It provides lessons in each subject area as well as essay prompts and sample essays.
PrepScholar breaks down the differences between the SAT and ACT tests.
Kaplan offers an ACT prep workbook on Amazon for less than $20.