I am reading this article, however, I am not sure if I've already grasped that article correctly or not, so I really need someone to confirm whether my understanding is correct or not.
First question
Suppose I want to tell everyone a pen belongs to me by saying "これは私のペンです." so just in case I lost it somewhere and someone found it, he will know that pen is mine.
Suppose there are 2 pens on the floor and then I pick mine and say "これがわたしのペンです."
Did I grasp it correctly?
Second question
In that linked article there is an example "日本語が上手ですね!" Can I change it using は as in "あなたの日本語は上手ですね!" without changing the meaning?
Did I grasp it correctly?
As you can tell from the length of the answers on the duplicate question, there can be no way to tell from two sentences whether you understood everything about は vs. が. Could you maybe try to ask a more concise question? For example, in which case が would be chosen over は to say that "this pen" rather than "that other pen" is "mine". – Earthliŋ♦ Oct 21 '16 at 12:44