English as a second language is quite difficult for many reasons. One important reason is that, unlike many other world languages, English is no longer an inflected language. Let me explain that to you. An inflected language is one where the form of a word determines its usage in a sentence. In uninflected English, it isn't word form we rely on for meaning and usage, but word order.
In a highly inflected language, the subject of a sentence can be at the beginning, in the middle, or even at the end of a sentence. Readers/Listeners know it is the subject because they recognize the form of the word, and that form tells the reader/listener "I am the subject of this sentence." Russian, Czech, and Latin are some examples of highly inflected languages. Most European languages are inflected as well, to some degree.
In English, though, the syntax (word order) in a sentence reveals the subject and the object, etc. For example: My friend ate a large meal. In most English sentences, the subject comes at the beginning ("friend"); it is followed by the verb, or predicate ("ate"); and what is called the object, or direct object of the verb, is at the end ("meal").
Breaking that sentence down to its simplest parts, then, yields
friend (subject) ate (verb/predicate) meal (direct object)
At one time, English was a highly inflected language, way back in the days when it was called Olde English. Old English came from its predecessor, Proto-Germanic. Both were highly inflected languages. However, as time went on (during the middle ages), English speakers stopped using the various forms of words that would indicate where it was a subject (nominative case) or an object (objective case), and they started using the same form for both usages. As a result, English speakers had to demonstrate a different way for listeners to figure out what the subject of the sentence was, so they relied on word order over word form. This put a special emphasis on the syntax of the sentence (word order).
Native language speakers internalize all the rules of grammar by the time they are 3 or 4 years old, and that is true with English-speaking children as well. No four-year old would look out the window and say, "Car see I a mommy!" They would say, "I see a car, Mommy!" That puts the words in the right order (proper syntax) with subject, verb, and object (I see car).
This is difficult for non-English speakers to internalize, because they have already internalized the inflected rules of their own language, and English is a real puzzle for them.
And... oh, I hate to tell you this... but it gets worse. During the Middle Ages, English was not a "respected" written language. Latin was the language of the educated, and students who went to school (not many did) learned Latin and its rules of grammar and syntax. By that time, though, the English language was already an uninflected language. That didn't stop the mathematicians and scientists who wanted to create a reliable system of grammar for the English language so that English would become more stable as a language and would develop into a "respectable" language that scholars could use.
Unfortunately, they decided to superimpose the rules of Latin grammar onto the English language. Of course, the rules of Latin did not actually fit English for two reasons: (1) Latin was inflected and English was not, so the forms wouldn't match up, and (2) English came from an entirely different language family (Proto-Germanic for English, Italic for Latin). Would you expect the rules to fit? No. And they don't. But we MAKE them fit. We take that square peg of Latin grammar and whack it by force into the round hole of English.
AND... as if all that doesn't make it hard enough to understand English, we are a language that stole words (uh... excuse me... borrowed words) from other languages. When English imported a word from another language, only one form of the word was brought into English from the foreign language, not the whole set of different forms that the word might have in its original language. So, over the years, English imported words from Scandinavian languages, from Latin, from French, and then from just about every other language under the sun, it seems. What a mess!
But that's what English has become: a hodgepodge of words from many languages with rules of grammar that don't actually fit, and then we tell our students to learn it.
English still has a number of inflected forms that have survived over the years. Perhaps the most obvious remnant can be found in our pronouns. Nominative case singular pronouns (used as subjects) include I, you, he, she, [and] it. If you see the word "I" in the sentence, you know that the verb (predicate) for that subject will be "am," not "are" or "is." Likewise if you need a singular Objective case personal pronoun, it will be one of these: me, you, him, her, it (you won't use I, he, or she as the object, just as you won't use me, him, or her as the subject.
All of this is complicated, I know, but I hope by sharing the reasons for English syntax being difficult for non-native English speakers, you will have a better approach to learning more of the language.
If I can help any further, please let me know.