The word you is a first-person singular pronoun. It can take the plural form you’re, used with a verb that agrees with it. It can also be used as a possessive, like yours, or a demonstrative adjective, such as your car.
You can use the article the with countable and uncountable nouns, but only when you and your reader/listener know about the specific noun you are referring to. For example, you can use the article the before a meeting that you and your audience/reader will be attending this afternoon.
In modern English, the distinction between the singular and plural forms of you was originally signaled by verb agreement. However, this began to break down in the 16th century. At that time, the thou and you distinction marked a close or personal relationship or a superior-to-inferior relationship. These forms were also more respectful and deferential than the you form, which became common for casual or familiar relationships.
You can still hear the thou and you distinction in some regional dialects of English. For instance, y’all (pronounced as one syllable) is the standard plural form in some Southern regions of the United States. Similarly, you-uns, yez, and youse are also used in some regional varieties of English. However, they are becoming less and less common as more people adopt a standard form of you.
Another important thing to remember about you is that it can be either countable or uncountable. Countable nouns have both a singular and a plural form, whereas uncountable nouns do not have a plural form. For example, the word exam is a countable noun because you can have more than one exam. On the other hand, the word concentration is an uncountable noun because it would not make sense to speak of having multiple concentrations.