All the sentences you have learned so far would never actually be used in Korean because they are not conjugated. I felt you needed to know basic sentence structure before you learned how to conjugate. The good news, however, is that conjugating in Korean is much easier than other languages (including English).
An important note before you begin
This lesson will show you how to conjugate past/present/future in the most basic way. Although all of these conjugations are grammatically correct, they are rarely used in conversations. This form is sometimes called "diary form" because it is usually used when writing to yourself in a diary. It is also used when writing tests, books (not in dialogue), research papers, newspaper articles, magazine articles, and other times when one is not speaking/writing to a specific audience. It is also sometimes called the "plain form."
If you used this form in a sentence, you should use the informal 나, as this conjugation is seen as informal. As such, throughout this lesson you will see the word 나 used for "I." However, as I mentioned, this conjugation form is also used in print (books, newspapers, articles, etc...). When this is done, the sentence is neither formal or informal – as it is just relaying facts. When used like this, no specific person is the speaker, and nobody is getting directly spoken to. Therefore you don't generally see 저 and 나 in these forms of Korean, and there is no need to see these writings as formal or informal.
It is possible to use this "diary" or "plain" form in conversation, but you are more likely to hear one of the conjugations discussed in the next lesson. Although the plain form is not very common in conversation, the conjugation itself is incredibly important if you want to understand more complex grammar later on or learn to read most printed forms of Korean (books, newspaper, etc...).
The only part of speech that gets conjugated in Korean is verbs and adjectives (and 이다). As you already know, a sentence must end in either a verb or adjective or 이다.
Let's look at how to conjugate verbs and adjectives into the past, present and future tenses.

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LEARN KOREAN (한국어) [GRAMMAR] #1
RandomThis is book #1 for the Korean Language series. Try to understand all of the notes in this book before you proceed to the next one. Good luck ! This book contains Korean grammar. Try to understand it so that you can understand how to make a sentence...