。
He plastered posters all over the wall.
Literal
He [topic-は] wall one-surface [to-に] posters [object-を] sticky-sticky pasted.
べたべた is a mimetic for sticky, messy adhesion — here describing the act of sloppily plastering posters everywhere. 壁一面に ('on the entire surface of the wall') uses 一面 as a spatial complement. 張った is the past tense of 張る ('to paste, to stick'). The mimetic adds the connotation that the result is messy and excessive, not neatly arranged.