There is a proof from a book I have a doubt on, but the proof itself is quite long. Should I copy paste the whole text or can I just take screen shot from the pages in the book and put?
You should transcribe the part of the proof you are confused about into MathJax, instead of taking screenshot, since screen-shots are not searchable. Then, if there are any terms in the section you transcribed whose definitions appear elsewhere in the paper, you should also transcribe their definitions from the paper into your question. Finally, try your best to explain what you are confused about.
If this is too much work, then it means that your question cannot be appropriately answered on MSE.