MATLAB is not a free-of-charge software. You need to pay for it. If you are a student you could look here to buy a license which will allow you to select the basic components of MATLAB/SIMULINK and you can add more stuff to it (of course paying it).
Some universities have agreements with Mathworks and they provide students with free licenses.
Check on the website of your university, where they provide softwares for students, if they have also some version of Matlab.