What would be good alternatives that could replace the word "fuel?"

Is it okay to say "shut up" to girlfriend? Isn't it too bad word?

I do not recommend saying "shut up" to a girlfriend, boyfriend, or in general. "Shut up" is a phrase that is considered aggressive and rude. Here, the speaker is saying "shut up" in a playful way rather than an aggressive way, because he wants his girlfriend to stop talking so he can kiss her.

What does the word "little" in "little people" mean? I was curious because it doesn't look like talking about the size of people!

Quite right! "Little people" doesn't refer to the size of the people themselves. There are two possibilities here, both valid. Belle could be referring to the number of people or population in the village. Or, she is saying that they are "small" in their thinking. They don't think too broadly about things and their lives that aren't too big or "flashy". Their exposure to the outside world is limited. They go around doing what they need to do every day. Ex: The population of our town isn't that big. There are like 50 families. Ex: Just because I'm from a small town doesn't mean I don't have big dreams! Ex: My life sometimes feels little and insignificant, but I know I have a purpose.

What's "Airstream"?

Airstream is an American brand which makes caravans or RVs. The brand is easily recognized by the distinctive shape of their rounded and polished aluminum caravans. These days a lot of people are buying and renovating old caravans as Airstreams are popular because of their shape.

What's the difference between "If you would" and "if you want"?

"Would" here refers to "would like", which has the same meaning as "want". The only major difference between "would like" and "want" is the formality. "Would like" is much more polite and less demanding than "want". If you tell someone that you "want" something, it is very direct compared to "would like", and can be seen as a demand. Ex: I would like a cup of tea, please. Ex: I want some water.

If I change "where" to "which" or "that", does the meaning change?

You can replace "where" here with "in which". Another way to say this sentence is, "What do you do to get all girls to hate us?"