「見せる」 (miseru) means "to show." You use it when you let someone see something, or display something. For instance, "写真を見せます" (Shashin o misemasu) means "I show a photo." It's the transitive form of "見る" (miru - to see).

「見(み)せる」は、何(なに)かを相(あい)手(て)に「見(み)せる」ことです。写(しゃ)真(しん)を見(み)せます。