My English teacher say that our setences usually include lots of things. Like this In the morning, I go to school to learn the knowledge about finance that is very important to me in the future. Compare with our writing, foreigners only tell one thing in a sentence .
But my last English teacher telled us,we should try to make sentences more beautiful and longer.
What should I do?
The sentences in your post are appropriate length. As your English improves, you will be able to write longer sentences without having them seem awkward.
The key is to read a lot. You will get a better idea that way of how much information English writers usually put into a sentence.