In English you add an apostrophe in contractions like can’t and don’t to show that a letter is missing. Portuguese combines words so they are shorter or easier to pronounce, but they don’t use apostrophes.
Remembering to use these in Portuguese can be tricky, but don’t worry! If you miss some contractions when you speak, people will still understand you!
Take a look at combining em + o. Em means in/on and o means the, But em o doesn’t exist in Portuguese, they use the contraction no:
no banheiro in the bathroom
no quarto in the room
no teto on the roof
Take a look what happens with feminine nouns, Instead of no, you have na, nos (masculine plural) and nas (feminine plural)
na mesa on the table
nos livros in books
nas praias on beaches