What does the Linux Command update do?

I'm still new to Linux, and have only entered "update" on Parrot OS in the terminal. Now my age-old laptop has been dumping things for ages. I thought to update the software would need another command!

"apt-get update" updates the package sources

https://wiki.ubuntuusers.de/apt/apt-get/#apt-get-update

With update do you update the packages.

Thanks, but I already know that. But I only entered update.

If you need help, enter the man command before the other command:

man update