What Are Differences Between Developing,developed And Underdeveloped Countries?

Developed countries have infrastructure in place- such as roads, bridges, water pipes, fuel lines, electrical wiring, fiber optic wiring, and septic/sewage and runoff drainage or treatment systems, to name a few- and the technical capacity to take care of all their citizens with such infrastructure services as mechanical repair or maintenance facilities, doctors and medical facilities, etc.  In short, a developed country has three things: It has stuff, it has people to take care of that stuff (and of other people), and it has people who make money and give up part of that money to pay for stuff.

a good example is south korea.

a developing country is largely similar, but the existing infrastructure is usually either old or poorly maintained (or both), and the people have less money to spend on stuff and so there are either fewer experts or the quality of the products that they make or the services they provide is lower than in a developed country.

a good example is thailand.

an underdeveloped country has lots of people, but lacks some (or all!) basic infrastructures for some or all of its citizens, and so the people have no stuff and must make money which they are then expected to give to their government, who will then give them stuff.  This doesn't often happen, however, because governments in these kinds of countries are invariably so corrupt that calling them 'governments' at all is ridiculous.

a good example is cambodia, burma, or laos.