ASL is the visual language used by many deaf and hard-of-hearing people in the United States and many parts of Canada.
ASL is very different from English–it is a complete language with its own grammar and syntax.
For more information, see the National Association of the Deaf's definition of ASL: https://www.nad.org/resources/american-sign-language/what-is-american-sign-language/.
RIT's ASL Video Dictionary and Inflection Guide: https://www.rit.edu/ntid/dictionary/app
RIT ASL & Deaf Studies Community Center: https://www.rit.edu/ntid/radscc/
Online ASL videos: http://www.ntid.rit.edu/aslie/current-students/asl-resources
Online Deaf Culture videos: http://www.ntid.rit.edu/aslie/current-students/deaf-culture-resources