How can we know God? Isn't God unknowable? We learn and study and follow God's commands and pray, but how do we know God (as opposed to what God wants)?
What is a true way to know GOD better? Which commands in Torah are related to my question?
Like anything in a relationship, it can only be partially captured or described in words. We still learn a lot from others before and around us in the way that they've known Him, so here are some thoughts.
The essence of your question seems to come from the fact that God is not part of creation, nor truly comparable to anything else in our experience of nature. We can't define His essence and we can't perceive with our minds or our senses the fulness of who He is. We know how to have a relationship with other humans, but how can we truly know someone who is not at all human; not even a part of the world around us, but in fact its Creator? He is not abstract or vague or senseless in who He actually is, but in our eyes He is beyond all our categories and imagination.
In the book Building a Sanctuary in the Heart (available online at bilvavi.net), there's a quote that struck me when I read it: "He is hidden from their intellects, yet revealed in their hearts." I asked a rabbi about this and he replied that even though our minds and senses can't perceive God's 'essence', we perceive His actions and can grow to understand them. And as the rabbi understood it, when we think about His actions our hearts get to know Him. A lot of the strongest, most tangible metaphors of God's actions in Judaism and in our everyday lives stand to this effect. Not in the sense of defining Him, but in the sense of His love for us. When people study His Torah, and step out into living it in real life, their hearts get to feel His holiness. When you accept His blessings in creation, from each breath, to everything you eat and drink, to the ability to trust and thank Him for His wisdom in every part of life (as in Psalm 139), you strengthen your knowledge of who you are as a creation and of who He is as Creator and giver.
Even though we can't understand the process of creation in general, we can see that it exists. In the same way, we can't understand how humans could have a relationship with God, but Tanach and the Jewish testimony about God narrate the creation of such a relationship in the world. If you can accept this testimony, you find that obedience to God is another way of knowing Him: using our ability to choose His ways allows us to draw closer to Him in both love and experience. The cause and effect of such a thing is beyond our speculation, but the reality is something we experience. Righteousness, justice, purity, kindness, and obedience that is either natural or costly to us; every connection with these things is an immediate connection with God.
So in both thankfulness for His actions and obedience to His ways in wisdom, Judaism spends a lot of energy and focus on the belief that God has made ways for humanity to know Him. He is hidden to our minds, but His actions aren't, and He is known by heart. Knowledge itself is a wide and varied thing: you can have intellectual knowledge, but also relational knowledge; you can know something distantly as a fact, or you can be deeply aware of it often. These kinds of knowing are connected in our experience. And kind of like in a human relationship, where we know some things about the other and there's a lot left to learn about them, we can still say it is them that we love and connect with. From God, this is a gift.
I'll note that I'm not Jewish and don't know a lot about Judaism, so I never post comments on this site... but these are some things that relate closely to the question and that I think are valuable.
Edit: I heard a six year old Jewish boy recently tell me that your neshama can see God. I thought it was a good way to put it (he learnt it at school, I think).
Ramchal in Derekh HaShem starts by repeating this statement of the Rambam and goes onto say that HaShem’s true nature cannot be understood by any other being than Himself.
Rabbi Yosef Dov Soloveitchik in his sefer Al Hateshuvah (my rough translation from the Hebrew) suggests this requirement to know that there is a Primary Being etc. does not mean philosophic reflection. It rather means a knowledge of and fixed orientation towards the reality of HaShem. The result is that in all times, good or less good, a person lives with the knowledge that HaShem is with him.
I have heard that the best way to come close to HaShem is through the Torah because it was always HaShem's precious plaything.
So by learning the Torah we comes to a closeness to HaShem
We are explicitly instructed in the Torah to "know" God. Deuteronomy 4:39:
Note: This answer was written in response to the initial version of the OP's question. At the time, I felt that the question was more than a little overly broad, and overlapped material from several other questions (which I posted in the comments). This answer was written specifically in response to the OP's statement that "in the end, we cant know GOD." Of course, much depends on exactly what we mean by "knowing God" (which was, and remains, unclear in the question). Nevertheless, the Torah clearly sees some degree of knowledge of God as both possible and obligatory.
Shaar Yichud chapter 4 "Any matter which one would like to understand when one is in doubt of its very existence, must first ask "does it exist or not?" After one has established its existence, one must then enquire as to what it is, how it is, and why it is. But regarding the Creator, a man may only ask whether He exists. And when His existence is demonstrated through rational investigation, we may further enquire whether He is one or more than one. And when it is clear that He is one, we may enquire on the matter of unity, and on how many ways this term is used, and in this way we will establish for ourselves the complete recognition of the unity of G-d, as the verse says: "Hear O Israel, the L-ord is our G-d, the L-ord is One" (Devarim 6:4)." (see the rest of the gate for more)
so according to this, we cannot know God. It is not within our ability. But we can know whether He exists and whether He is more than one, but only through rational investigation. It is not possible to see God since He is infinite, and with our finite senses, we can only see finite things.