What's the difference between もちろん＆もちろんです?
"です" makes it polite. I would stick to polite language until you have more experience in the language, so try to use です (or ます forms for verbs) when you can.
Just echoing YozakuraHime's answer. Similar to the difference between 'Of course' and 'Of course it is'. No difference in meaning or nuance. Just a grammatical difference. I would also agree to stick to 丁寧語 (ていねいご - polite language）by using です or ます by default.