From The TimeSplitters Wiki

A Power-Up is an item used to give the player who has obtained it special abilities for a short time. Power-Ups are usually small floating orbs with different symbols and colors to signify their effect. They are activated simply by walking into them. Power-Ups are always available unless they have been disabled in the match options or if you have not placed any on a Mapmaker map.

Power-ups are not included in TimeSplitters, and are usually only available in Arcade Custom and MapMaker modes in TimeSplitters 2 and TimeSplitters: Future Perfect.