"A fat dog is slow."
Translation:Un câine gras este încet.
Because câine is a masculine noun, while pâine is a feminine one. The ending doesn't help figuring this out, you just have to know their genders. I know it is difficult.
It is difficult for me too when I'm learning Spanish or French because I assume their nouns have the same genders I've associated them in my mind, yet they very often do not.