Linguistics is the systematic study of how language works. Linguists work on sound systems (phonetics and phonology), on the relationship between form and meaning (morphology, syntax, and semantics), and on how languages change over time.
In introductory-level Linguistics courses, you study language systems by analyzing data from languages of contrasting structure. You can expect to study English, but also languages like Cantonese, local First Nations languages, Latin, or Haitian Creole.