How does the creature say he learned to live in the world in Frankenstein?
According to the summary available at the link below, Frankenstein comes to a point where he is able to merge his feelings about how much he can push the boundaries of science and in some sense mimic God in creating life, he also finds limits to that.
Although Frankenstein had a duty to his creation, he felt his greater duty was to humankind, to protect them from the terror and destruction that themonster and a companion might create. In fulfilling his duty to mankind and refusing the monster's request for a companion, Frankenstein brought the monster's wrath upon himself and his family. Frankenstein tells Walton to "'[s]eek happiness in tranquility and avoid ambition, even if it be only the apparently innocent one of distinguishing yourself in science and discoveries.'"
So, by the end of the story, he has learned that everything must in some ways be done in moderation. His duty to humankind as a scientist in terms of constantly pushing the boundaries is tempered by his duty to humankind as a fellow human and as such one who should not necessarily unleash on them the monstrosity that he considered Frankenstein.
He learns the same way we learn-by experience. Of course, he is at a disadvantage, having no parent there to guide him through his trials. But he slowly learns to "distinguish [his] sensations from each other": recognizing forms, light, sound, etc. He also learns to use tools, wielding fire to his advantage after burning himself once.
One day, when I was oppressed by cold, I found a fire which had been left by some wandering beggars, and was overcome with delight at the warmth I experienced from it. In my joy I thrust my hand into the live embers, but quickly drew it out again with a cry of pain. How strange, I thought, that the same cause should produce such opposite effects! I examined the materials of the fire, and to my joy found it to be composed of wood.
Essentially, he learns scientifically, through observation. These chapters represent a child taking his/her first steps in the world, slowly discerning each new sensation.
You tag this with the phrase "the monster" so I wonder if you are asking about the monster (which is not really called Frankenstein). The question makes more sense to me this way than if you were asking about Victor since it is the monster who really has to learn about the world.
The monster learns about the world mainly by observing the people in the village. He learns from them how to speak and read and such. Then he learns about other stuff from books.
He does not actually say "I learned to live in the world" at any point, but he does tell how he learned various things. This starts in Chapter 11 and goes on through Chapter 16.