In Matthews10:34 it says:"Think not that I am come to send peace~" But why is the grammer so wierd?

This is nothing more than sentence structure based upon the language in use at the time of the translation. The sentence structure is from the King James Version. The Greek (the original language that this was written in) is written “Not think that I came to bring peace on the earth: not I came to bring peace, but a sword.
“I came” and “to bring” in the Greek is one word.
The sentence structure you submitted is only found in the KJV. All others have it as “I have come” or “I came”

The “I am” in the sentence structure is not to be understood as in John 8:58, Jesus said to them, "Truly, truly, I say to you, before Abraham was born, I am." This word I am is found in the burning bush speaking with Abraham, “I am that I am.”

Here, Jesus is making a definite statement that He in fact is equal with God the Father. This is His final statement of a debate, rather a challenge, that began in John 8:3 “The scribes and the Pharisees brought a woman who had been caught in adultery.” Read the whole passage and see it escalate to His climatic answer.

The religious leaders clearly knew that He was saying that He is equal with God the Father and that is why they picked up the stones to kill him. There was no misunderstanding of what Jesus said. This very statement by Jesus identifies all those who claim that Jesus is not God as “wolves” or “false teachers.”

You may also find this interesting if you would like one more example of how important it is to know as best as possible the meaning of the original words. Read Jn. 18:1-11 Again there is written “I am.” V6 When he said to them, "I am he," they drew back and fell to the ground.”

Standing before Jesus is 400 or more soldiers, guards, religious leaders and busybodies. All of these people didn’t take a step backward and trip. The word fell has, in its definition, the meaning forcibly, like being pushed.

It is Jesus who created everything that exists, Jn 1, by the will of the Father and by the power of the Holy Spirit and He spoke everything into existence. So here, when He spoke to this crowd who came to arrest him, He spoke with ever so slight of power, just enough to knock every one of them to the ground.

And Peter, seeing all of this happening, rises to the occasion to prove Jesus wrong. Jesus had recently told Peter that he was going to deny Jesus. Peter had one of the two swords, and here with every one already on the ground, he saw the perfect opportunity to demonstrate to Jesus that he would defend Him, so he drew out his sword to separate in two the head of the first one he came to, who was struggling, probably on all fours, to get up. But he missed his target and only cut of the ear.

Hope this helps, from a student forever.