So I have been doing German for a little while and I my stage they mainly do just 2 cases, but I still find it very difficult to find out which way I am supposed to change my words based on which context they are used in, so I mostly just guess. But does anyone have any tips.
The exact form of each noun/pronoun and their adjective/article depends on grammatical gender and case
To find out what the case is, you have to look at the function the word fulfills in the sentence. You can figure out the function mostly by looking at the verb. Each verb expects a certain number of components to go with it, ie. subject, direct object, indirect object...
subjects (and objects for the verb "sein") use the Nominativ case.
direct objects (and prepositions that indicate destination) use the Akkusativ case.
indirect objects (and prepositions that indicate position) use the Dativ case.
when indicating ownership or affiliation, and for some verb objects, use the Genitiv case.
to differentiate between direct and indirect objects, you'll have to learn how each individual verb is used and what its meaning is.
Once you've figured out case and gender, you decline your words according to something like this
which you will have to memorise eventually.