mandarin use simple chinese, cantonese use traditional chinese. some of them look the same, some are far different. even some chinese don't understand cantonese without learning. wish u all good!

Chinese character is universally used in both Mandarin & Cantonese, also used in Wunese, Minnanese & Hakka. But some characters, which are only used in Cantonese, won't be found out in Mandarin or other Chinese languages. I mean, if you could master Chinese characters as many as possible, it would be of great help for you to learn Mandarin & Cantonese. It's just like that, for example, you know the number from 1 to 10, Maybe 1-5 are often used in Mandarin, but 6-7 often used in Cantonese, 8-9 in Minnanses, & 10 in Wunese.

For example: 呢 means "this", 呢度 means "here", & "this place" in Cantonese. But in Mandarin, 呢 is only a modal word which expresses the mood of sentences. Could you understand what I said?

While learning Cantonese, you'll probably find that, there're a lot of characters which usually have a "口" in the left, such as “哋、啲、呢、咩、嘅、叻” ......(not used in Mandarin), & as well as some characters which are not used very often in Mandarin.

BTW, I suggest you learn Simplified characters, because it's easier for foreign learners.