Not sure about spanish, but in portuguese, as a general rule, you decide the gender of an object by the last caracther. For instance “cadeira” (chair) is feminine while “livro” (book) is masculine.
Basically, most feminine words end with an “a” while masculine words end with an “o”, although there are some words that end with other letters whose genders is not that easy to identify. For instance “árvore” (tree) ends with an “e” and is feminine (“a árvore”), while “peixe” (fish) also ends with an “e” but is masculine (“o peixe“).
Basically, most feminine words end with an “a” while masculine words end with an “o”, although there are some words that end with other letters whose genders is not that easy to identify. For instance “árvore” (tree) ends with an “e” and is feminine (“a árvore”), while “peixe” (fish) also ends with an “e” but is masculine (“o peixe“).