There isn't an idiom called "high fore." Try to figure out exactly what you heard or read, and type in another question so we can answer it.
a mass where prayers are sung
I'm not sure what you mean by "italicized expression" here -- that term just means something that is printed in italic font.I also think maybe you mean OPPORTUNITY, which is not an idiom.
No, it is a description of what to do to butter when you are cooking - make a light cream out of it by stirring gently.
If something is done at the eleventh hour it is done at the last possible moment. The implication is that the deadline is twelve o'clock.