Places, people and things are all nouns, e.g. "corner", "vicar" and "tree". If you can put "the" or "a" in front of a word then it's probably a noun. Nouns are essential in English.
Can you write sentences without nouns? Just about! Consider these examples: "Smile!", "Stop!", "Run quickly!", "Stir briskly." Notice anything? These are complete sentences, but what do they have in common? They are injunctions, or orders. Each has a verb, with perhaps an adverb. If you want to say anything more than this bare bit of information, you will need to begin adding nouns: for example, "Stir the batter briskly." Here the noun is "batter". Or you might say, "Stir the batter briskly with a wooden spoon", adding two nouns, "batter" and "spoon".
If you can replace a word with "it" or "he/she/they/you/we", it is a noun. These words which can replace nouns are called "pronouns".
Test your knowledge of basic nouns by playing this quiz on the subject.