"Você precisa deste livro?"
Translation:Do you need this book?
It can be confusing. Precisar is a verb and just like an English verb it changes depending on the tense. The changes in Portuguese are much more extensive than in English though. Here we need the form (conjugation) of precisar for the present tense that matches "você" and that is "precisa". There is a word "preciso" but that is the version of precisar that goes with "I". So although one ends in "a" and one ends in "o" it doesn't indicate gender.