The word "tongue" here is a synecdoche for all the parts of the body which a person uses in order to speak. (See: [[rc://en/ta/man/jit/figs-synecdoche]])
Clear speech is language that people can understand. Paul was talking about people speaking in other languages during church services. Alternate translation: "If you speak in a language that people do not know"
These passive clauses can be translated in active form. Alternate translation: "how will anyone understand what you have said" (See: [[rc://en/ta/man/jit/figs-activepassive]])