Hi and welcome to the Julia discourse.
Could you maybe provide code that is not working? As Daniel wrote, you might have (just) added a package (installed it on hard drive) but not loaded it (using).
Also – which package you did add would be good to know (see also Please read: make it easier to help you for more details).
Two formatting tips: You can put code in backticks ` to have inline code (or three of them to have a code block) – and you can also put math in $...$ to have it rendered like $\alpha$ renders nicely as \alpha.