A Coursera Specialization is a micro-credential offered by Coursera which is made of several courses. In some cases, the final course is a Capstone project which is assessed by student peers. Most specializations have 4 or 5 courses, although some have up to 10. Most specializations take 4-6 months to complete.
To earn a specialization certificate, you need to pay for all the courses and complete the necessary work. Individual courses can be taken separately but capstone projects are not available unless you have completed all the other courses in the specialization.
Many Specializations run on a subscription basis costing between US$39-79 per month (https://about.coursera.org/). Most offer a 7-day free trial, after which you will be billed. If you cancel within the free trial time, you will not be billed, unless you have completed a course and received your certificate. If you decide not to complete a Specialization, make sure you cancel your subscription, or you may continue to be billed.