English itself has not much basic messages to use in daily communication. We can simply say some easy sentences to our friends or colleagues. And that we can understand each other. But on our way of studying English, we must face with too many rules and exceptions. We can notice this from any exercise, it has a lot of pitfalls waiting for us. That make learners (not me) get bored and give up studying English.
Are you being forced to learn English or was it your choice?
If it was your choice and you decide that you have made a poor choice, then you are free to give up.
If you are required to learn English, my advice is to make yourself be more enthusiastic about it. Become interested in the language, the grammar, the form, the rhythm, everything about it. See it as a challenge that you really want to win. Prove to yourself and to others that, even though you see English as very difficult to learn, you can do it.
You said "our way of studying English". Can you find different classes? Do you have a native English speaker somewhere nearby who you can talk to for an hour or so twice a week? Do you read English websites and newspapers? Trying to learn English just from a book is difficult, that's true. You need to surround yourself with the real language whenever possible.
In answer to your original question, yes, it's necessary to add "s" to third person singular present tense verb forms. No, we don't know why. That's just how it is. As Soothing Dave pointed out, conjugating of English verbs is actually very simple compared to many other languages where the verb form is different for every person in every tense. There are far more complicated things to learn about English.
We understand your frustration but this website can be your friend. We are here to help you with specific questions and problems that you have with your English study. To be honest, though, if you don't post questions that we can answer and you simply post messages complaining about the language etc, there is little we will be able to do for you.
I hope you will be able to change your way of thinking about English - learn to enjoy studying it!