Basic Roman numerals are actually really easy to learn.
I that's one. V is five. So if you have II it's two and so on with three and four would be IV because it's one before five which is 4. Six being VI one after five and so on until you get to ten which I think is X but I'm not sure.
Fun fact: A lot of Romans actually didn't write 4 as IV but as IIII. When you are in rome you can often see this in old ruins of temples and other buildings.
I that's one. V is five. So if you have II it's two and so on with three and four would be IV because it's one before five which is 4. Six being VI one after five and so on until you get to ten which I think is X but I'm not sure.