Stress when changing case
Does the stress of a word change if a suffix is added when changing case (стол -> стола)?
Unfortunately, it depends on the word. In the case of the word "cтол", the stress does indeed change, so it would be "столА". But for example, in a word like telephone (телефон), the stress is fixed. (телефОн -> телефОна) There isn't really a clear easy way to know when the stress changes and when the stress is fixed, so it's very important to practice aloud how the words sound in different cases. Good luck! :)
You might want to have a look at this discussion: https://www.duolingo.com/comment/12202471
It's not very helpful because you still have to know the stress pattern of each word. And they are not very predictable... :(