They all have same meaning "but" . but "par" has another meaning "wings". you can use any on these words because they chosen according to the ease of spoken pace.

There is no difference among these three words. The three words are synonymous, they mean the same thing i.e. "but".

depending on situation and how do you apply

These all worlds are same meaning in english we say but for these three world all are excuses.

it is not like "not only ,but also" it is we use commonly as u use in English. like "I have car, but I don't have car key " just like that I would like to teach u .I also need to communicate in English would u like to help me?