Algebra is a branch of mathematics concerning the study of structure, relation and quantity. Learning algebra is a little like learning another language. By learning the simple language of algebra, mathematical models of real-world situations can be created and solved. These problems can't be solved by only using arithmetic. Instead of using words, algebra uses symbols to make statements.
In algebra, letters are often used to represent numbers. Algebra also uses the same symbols as arithmetic for adding, subtracting, multiplying and dividing.