The word ‘sofa’ in French is masculine. You would say ‘le sofa’ when referring to it.
In French, nouns are categorized as either masculine or feminine, and this often doesn’t correspond to gender in the way we think of it in English. The gender of a noun affects how you use adjectives and articles in sentences. For example, since ‘sofa’ is masculine, you would use masculine articles and adjectives when describing it, such as ‘le beau sofa’ (the beautiful sofa).
It’s helpful to memorize the gender of nouns as you learn the language, as it can change the way you form sentences. Some learners find it useful to associate certain endings with masculine or feminine nouns, but there are many exceptions, so exposure to the language is key.