What does S il vous plait mean in English?

"Please" is an English equivalent of the French phrase "S'il vous plaît."

Specifically, the conjunction "si"* means "if." The personal pronoun "il" means "he, it." The personal pronoun "vous" means "you." The verb "plaît" means "(He/she/it) does please, is pleasing to, pleases."

The pronunciation is "seel voo pleh."

*The vowel "i" drops before a subject that begins with a vowel. The temporary nature of that drop is indicated by an apostrophe immediately after the article and immediately before the following subject.