If you have in mind there is no company that is ready to sign a contract, you must contact the school Director. It can give you necessary recommendations and sends the application to the municipality, which receives all the proposals employers.

Otherwise, you can just cut to the chase and to negotiate with the right company.
After that, you are likely to be invited for interview to signing the contract. Carefully read the terms and conditions of the contract. If you are under 18 years of age, when signing the agreement must be accompanied by a parent or guardian.
The contract must be signed by both parties and sealed with the seal of the company. In addition, the agreement must specify the school, faculty and speciality, which is sent to the applicant.