Learn Portuguese (Portugal): Eu gosto de ler no quarto.

In Portuguese, the verb gostar (to like) almost always requires the preposition de right after it. While in English you just say "I like to read", in Portuguese the structure is closer to "I like of to read". You will use gostar de whether you are talking about liking an action or liking a thing.

Why is ler in its basic, unchanged form?

Because gosto is already conjugated to match Eu (I). When you connect two verbs to express what you like to do, only the first verb changes to match the person. The action you like doing stays in the infinitive (the basic dictionary form), which in this case is ler (to read).

The translation says "in the", but the Portuguese word is no. Where does that come from?

This is a contraction you might remember from earlier lessons. In Portuguese, the preposition em (in/on/at) must blend with the word for "the" if it comes right after it. Because quarto (bedroom) is a masculine word, "the bedroom" is o quarto. When you combine em + o, they merge into no.

Can I leave out the word Eu?