The first two are just increases or decreases in an amount of money. The third one means to make progress. It probably came from the way wars used to be fought: a line of soldiers fights another line of soldiers. When one line moves forward, they have "gained ground." The phrase lost relevance in war, and now it just means you are doing something against an opposing force, and you have made progress.

These all concern money. To relate to the answers, you would have to think of the time when 1 dong was a significant amount of money and 100 Su were required to make 1 dong.