The phrasal verb "get by" has several meanings. To "get by on" implies to manage to exist using some resource. "I get by on five dollars a week".

Hi! I will try to answer your question. To "get by" means to succeed, but only barely. I am getting by if the money I earn at work only pays for my basic needs (food, water), but nothing more. To get by of course is also used in a literal sense. If I am in a crowded place, I may have to "get by" somebody to reach a destination. In this sense, getting by means to move past. I hope this helped!

To have sufficient resources, would be the definition. Examples: I do not have enough money to get by this week. Can we get by on the food in your refrigerator? Can we get by on the water we are hiking into the desert with? Can anyone get by on just the bare minimum of love and care?