Spacing problem in Word

I have a sentence that I've copied and pasted from one document to a new Word page that stretches past the margins of the new page.  If I put the icon in front of part of the sentence with the idea of clicking Return and moving it to the next line, it does move, but it double-spaces and there is no way for me to get it back to a single-space paragraph.  I have gone through the selection process of selecting 1.0 for line spacing, but it doesn't do anything.