The word "uso" is the verb "usar" ("to wear") conjugated in the present "yo" form. You would write "usa" to say, for example, "She doesn't wear elegant clothes" ("Ella no usa ropa elegante"). All of the conjugations of usar would be:
-Yo uso = I wear
-Tú usas = You wear
-Él/ella/usted usa = He/she/you (formal) wear
-Ellos/ellas/ustedes usan = They (male or mixed)/they (all female)/all of you wear
-Nosotros usamos = We wear
Hope that helps!