Previously we have seen se as a reflexive verb pronoun. Se can be used to talk about activities for which the subject in general, that it is not specific or it is unknown. We will use the costructin of such will be se + verb construction. Se sentence contruction in the passive voice, when the subject is unknown the verb will be in the 3rd person singularl (él/ell/usted), but if if refers to a plural noun, then the verb will be in the plural third person form (ellos/ellas/ustedes).
Se prohíbe fumar Smoing is prohibited
Se vende camisa Hawaiyana Hawaian shirt sold here
Se venden camisas de traje Dress shirts are sold here