How to work the Polish Grammar and Cases?
for me it's difficult to use the words of a sentence. can anyone help with that?
Did you mean that it's difficult to form a correct sentence out of words that you learned?
You can't learn all the grammar all at once, so I would recommend that you get an exercise book and practice every grammar topic individually. If you need to look up grammar conventions and rules, you can use those sources:
For verb conjugations and noun declensions I would recommend to use the English wiktionary.