Answer:
Brazil: most of the Brazilian population lives by the Atlantic coast, or near inland. The Brazilian coasts are characterized by a tropical climate in the north, and a subtropical climate in the south. They are not very mountainous except for a few areas in states like Rio de Janeiro or Santa Catarina. In other words, the land is suitable for settlement.
A few Brazilians live farther inland, in the arid plains of the Mato Grosso, or in the tropical rainforest of the Amazon. These areas have less suitable climate and soil, hence why less people live there.
Japan: Japan is an archipelago consisting of relatively small islands that are very mountainous and very forested. Japan is also the 11th most populated country in the world, with around 125 million people.
For this reason, most of the Japanese live in very dense urban areas like Tokyo, Osaka or Nagoya. A few Japanese live in rural areas, in smaller cities and villages, although many of these places are suffering from depopulation due to Japanese low birth rates, and internal migration.
Egypt: almost the entirety of the Egyptian population either in the Nile river Delta, or along its course, and this has been the case since antiquity. The reason is very simple: the rest of Egypt is a inhospitable desert where no crops can be cultivated, where the terrain is essentially sand, and where the climate is extremely harsh.