What is best way to create variable in enviroment file?

In laravel I need to create variable in env file. According to documentation and some relevant threads (got after googling) I need to do add variables in .env file

I have tried following

SANDBOX_PAYPAL_CLIENT_ID=7I3D9
SANDBOX_PAYPAL_CLIENT_SECRET=S2E4C5R6E7T

I am confused that after adding here variable I just need to call then into controller or I need to setup again in somewhere ./config/ directory? What is best practice, can someone guide me about that. I would like to appreciate. Thank you

via Chebli Mohamed