, and welcome to Bleeping Computer.
Place your cursor at the beginning of what you want to copy.
Click the left mouse button, and hold it down.
While still holding the button, drag the cursor to the end of what you want to copy.
Release the left button.
This should have highlighted everything you wanted to copy.
Click the right button, and in the menu that appears, select Copy
Go to where you want to paste, what you just copied, and click the left mouse button, once.
Now, click the right button, again.
In the menu that appears, select Paste
What you previously copied, should appear.
You've just copied, and pasted.
That's all there is, to it.