"The friend teaches English to the dog."
Translation:친구가 개에게 영어를 가르칩니다.
I don't know if you still need help, but: It's a way of identifying it. 를 and 을 are used after the direct object and 은, 는, and 가 are used after the subject. 를 and 는 are if it ends in a vowel sound while 을 and 은 are used after consonants. 가 is used as more of "the" as in 남자가 "the man." 는 is like "a" as in 남자는 "a man." It's just more specific between the two. This might not be what you meant but I hope it helps!
If your friend is teaching English to a dog, they’re probably a little crazy in the head.
Because you're using every single particle on each word in this sentence, technically the words before the verb at the end of the sentence can come in any order. Though it's more typical to follow the SOV structure or, if not, words will be placed in order of importance.