Hey Japleen Singh ! Check out this blog. Basically,

After registering, students receive an email with their username, serial code and activation code for a specific version of Sage 50 (2014, 2015, 2016 or 2017 etc.)

https://www.sage.com/ca/about-us/education

Step 1: Open a web browser and go to http://reg.sage50accounting.ca/keyreg/student/

Step 2: Fill in the form with the required information.

Step 3: Wait for a confirmation email from Sage Education.

Step 4: Use the Serial number and Key code in the email to activate your Sage 50 program.

Step 5: These codes can be used again if ever you reinstall the program.

How to download the student version ?

After registering, make sure to download the Sage 50 software version that corresponds to your codes received in Step 3 see link: https://www.sage.com/ca/about-us/education

How to activate the student version?

The Student version has no Account ID, so if you encounter a field requiring this number during product activation then you've installed the regular version instead of the student version.

most of the steps i did and installed it i am having problem with the choosing the company. Please advice!

yes and its not and i downloaded from internet, please tell me the way to activate it fast. I have to complete my assignments 

To activate:

1. Launch Sage 50 Accounting .
2. Click Activate Now.
3. Enter the activation key code (CHECK your JunkMail**) for the registration email and click OK to activate your software.