Oliwia and Andrzej are right. Don't bother, it's a really common mistake and having read what Olivia and Andrzej's answers you already have better understanding of grammar than most Poles :).
In most cases the article takes after the last letter in the word. So: "tę książkę", "tę bluzę", "tę gitarę", "tę dziewczynę". However, there are some minor exceptions like: "tę służącą". Don't bother though, they are really rare.