If you're trying to use your company or educational institution's license, ask whoever maintains the organization's software licenses (probably someone in the IT department) for the instructions and information you need to access MATLAB and other MathWorks products.
If you've purchased your own license, you should have received an email from MathWorks with the instructions and information you need to access MATLAB and other MathWorks products. If you did not receive that email (check your spam folder) or if you have deleted it, please contact Customer Service using the Contact Support link at the end of this page.