as a proper noun, 'America' refers to specific entities, namely continents or countries. Proper nouns are always capitalized in English, and they refer to unique entities as opposed to common nouns which refer to a class of entities.
'America' can refer to
the continents of North and South America combined, a shorthand, especially in colloquial contexts, for the United States of America.
The voyages of Christopher Columbus led to the European discovery of America.
Many immigrants traveled to America in search of a better life in the 19th and 20th centuries.
Jazz originated in America and has since become popular worldwide.
While 'America' can refer to the combined continents of North and South America, it's often used, especially in everyday contexts, to refer specifically to the United States. This usage can be seen as ethnocentric, and it's essential to be aware of the context and audience when using 'America' in this way. When referring specifically to the United States, it's clearer to use 'the United States' or 'the U.S.' to avoid ambiguity.