I need to know what exactly CPU usage means

Good day.
Please, I need to know what exactly CPU usage means and if there’s a way for me to monitor it.
After two days of using it, I noticed that it’s already running around 16%, and I want to know what it means.
I have unlimited broadband and bandwidth but I have no idea what CPU usage is.
I have read negative reviews in Arvixe where CPUs and the accounts were either cancelled or blocked. I don’t want this to happen to me because I’m a starting in the service field and I want to make a good impression.
I just want to know if professional accounts are bound by the same rules such as Arvixe’s or if they are operating on a different platform.
I hope you can help me.
Thank you.
