Many people work in Brazil without an employment contract. However, as a foreigner you should require a contract from your employer as you will need it for your work visa and to work legally in Brazil.
Brazilians usually work on an “employee's record book” (Carteira de Trabalho e Previdência Social - CTPS) instead of a work contract. A detailed work contract is only common for managers and executives.
The employee's record serves at the same time as Social Insurance Identity Card. It contains all relevant information about the employment of each employee, e.g. the official position and function of the jobholder, the salary, pay rises, vacation times etc. The Carteira belongs to the employee and the employer has to hand it back immediately after entering the information.
You can apply for the Carteira de Trabalho e Previdência Social at the local Labour Department after your arrival in Brazil. You have to apply for your Foreigner's ID (CIE) first and you will receive a receipt which you have to show in order to obtain your CTPS.