The following is but a brief overview of one subject from French Grammar that may cause headache to Anglophones who are not accustomed to the idea of grammatical gender.
All French Nouns, whether referring to living beings or not, are either masculine or feminine in gender. The terms masculine and feminine genders mean grammatical ones and are not equivalent to the terms male and female. The ideas may overlap in certain cases (un homme = a man, une femme = a woman), but with the vast majority of nouns the masculine or feminine gender either has no connection with sex (un rat = a rat (of either sex), une souris = a mouse (of either sex)), or, in the case of inanimate objects, it is applied to nouns which cannot be considered as male or female (un fauteuil = an arm-chair, une chaise = a chair).
It is possible to list by meaning or spelling, certain classes of nouns as being likely to be masculine or feminine, however, the exceptions and complications are so numerous that the problem remains one of learning. Much time will be saved in the beginning of learning French if French nouns are invariably learnt with some accompanying word, such as the corresponding definite or indefinite article (le/la and un/une respectively) or other determiners. So here,
La porte = the door (note that in English inanimate objects are mostly
neutral with few archaic exceptions such as ship). La fenêtre = the window
La salle de bain = the bathroom
In English it is often possible to replace the genitive case in the case of nouns by juxtaposition of the nouns. Thus, instead of the door of the bathroom one says usually the bathroom door. This is not possible in French. The idea of the English possession (i.e. the genitive case) is given in French by de. That's why the answer of @Flying_whale contains de in the second part of the translations.
La porte de la salle de bain. La porte des toilettes (he door of the toilette). La fenêtre de la chambre (the widow of the bedroom).
The feminine of rat is rat(t)e (see comment).