What is the difference between Kamatz and Pataħ? (Niqquds)
As the title says I am trying to work out the difference between the two, can anyone help me?
No difference whatsoever in modern pronunciation. Originally patakh was probably closer to an o sound (judging by Ashkenazi and Yemenite traditional pronunciation). Eg. in Ashkenazi pronunciations of "kasher" you get "kosher" because of the patakh.
By the way, "nikud" is the name for the entire system so saying "nikuds" or "nikudim" sounds strange. It like how in English it sounds funny when a non-native speaker says something like "Tonight I will go to the gym and do some exercisings".
Native Hebrew speakers do not need or use Nikud for reading and writing. Most Hebrew texts are without Nikud. I'll even say that most of adults know how to read Nikud but need the dictionary to write it correctly. Nikud is been used in books for children, In the bible, in poetry and in rare cases in which without it the whole sentence will be ambiguous (and normally it will only use the Nikud needed to solve the ambiguity).
I've seen nikud being used too in books like Harry Potter, where there are words that are not of Hebrew origin like the names of the characters and the spells. Don't rely on that too much, because it's rarely used outside of dictionaries and children's books. At the beginning it'll be hard, but you'll get accustomed, that's what we did when we were children :)
In modern Hebrew there is no difference. Originally kamatz (constrict) would have been a sound closer to the a in the Farsi pronunciation of Iran where you constrict your mouth, while patach (open) would have been the same as the modern usage for it where you open your mouth.