I am writing a report in which I have to define some terminology. If I copy from any source and paste it and mention the source will it be enough or do I also have to mark inverted commas along with the source.
I'm assuming you mean "quote marks" as I've just used them. Yes, you need to indicate precisely what you have quoted (copied). The usual method is quote marks, but some other options are available if you make your intent clear. For example you can indent paragraphs like the following, indicating that it is a direct quote.
When in the course of human events...
Yes, if you directly copy text parts, you need to use quotation marks (the inverted commas) and cite the source.
However, in most cases it is better practise to not use a direct copy of the text with quotation marks, but do an indirect copy, i.e., you paraphrase the source material with your own words. Then you do not use qutation marks, you just cite the source. The reasons are that you can write a text that is better to read with the indirect copy method, and that you show that you have understood the source material by citing it with your own words.