also: しょんべんをする
expression, suru verb (irregular)
General expression for urinating. 小便 is a plain word; the whole phrase is neutral to informal. The reading しょんべん is more colloquial and can sound childish or rough.
トイレで小便をした。
I urinated in the toilet.
子どもが道端でしょんべんをしていた。
The child was peeing by the roadside.