It's not an idiom, it's a computer direction. "Opening" an attachment means clicking on the link and causing the attachment to upload to your computer.
That would depend on what the attachment was.
It means things are trustworthy.
About to be sold, or given up.
To make a mistake
say no to it
To keep struggling and not give up.
It means shut up!
flatter her to get something
he suddenly turned up (to appear, emarge)
to make something stronger ,,
It's not an idiom. To break camp means to break it up, to pack your things and leave the area. It can be used as slang, however, to mean a group "packing up" and leaving.
The idiom "crack someone up" means to make someone laugh or amuse them greatly.