As a complete beginner taking on Korean for the first time, you are often at the mercy of an incomprehensible, overwhelming flood of information that floats around the internet. Without knowing where to start, many have gotten discouraged to set their foot in the otherwise pleasant Korean learning journey.
Learning the Korean alphabet is one thing. Understanding and applying the Korean grammar is another thing that needs to be thoroughly taken care of. I would like to take the time to point out the major differences in the make up of a sentence in English and Korean.
Whereas in English the order of words is tremendously important, things are not quite the same in Korean. In Korean, there are particles which act as indicators of what sort of role proceeding nouns play. Let's take 이/가, one of the two groups of subject particles, for an example. Let us also imagine there is an imaginary person called Donald, which could be written in Korean as 도날드. In order to indicate Donald is the agent of an act, the subject, in a sentence, the subject particle, 가, is simply added right behind it: 도날드가; Depending on how the proceeding noun ends, whether in a consonant or a vowel, either of the two aforementioned subject particle follows; In this case, since the word, 도날드, ends in a vowel, the subject particle, 가, is added.
Another thing to keep in mind is that Korean is a predicate-final languages, meaning all sentences end with verbs or adjectives at the end. Let's make use of the transitive verb: to eat, 먹다 in Korean; Transitive verbs require objects to act on. Our job here is to translate the english sentence "Donald eats an apple" into Korean. (apple is 사과 in Korean) Taking into consideration the principle of ending a sentence with a verb, we are able to cook up a Korean equivalent: 도날드는 사과를 먹다 (를 is an object particle, which we will get into a later lesson). As you can see, the verb comes at the very last in the sentence.
One last thing to address is that Korean is a pronoun-drop language, meaning Korean does not make use of pronouns like she, he, it, they as much as English. During your Korean learning journey, you will more often than not run into a sentence without a subject. If we can deduce what the subject is in context, there is no need for a repeat.
The sentence 먹었다 (었 is a past-tense suffix) is a complete sentence in itself if the subject of the verb could be understood in context. Where in English, just saying "ate" is grammatically incorrect as the verb requires a subject like pronouns or nouns.
That was a crash course on the Korean grammar that is quite unique from English! I hope you have taken away the three key points!