As an adverb meaning "only" or "simply":
* Just a moment, please. (Solo un momento, por favor)
* I just want to say thank you. (Solo quiero darte las gracias)
* It's just a small problem. (Es solo un pequeño problema)
As an adverb meaning "recently" or "a short time ago":
* I just saw her. (La acabo de ver)
* They just arrived. (Acaban de llegar)
* We just finished eating. (Acabamos de comer)
As an adjective meaning "fair" or "right":
* That's just not fair! (¡Eso no es justo!)
* It's the just thing to do. (Es lo correcto)
As an adjective meaning "precisely" or "exactly":
* He arrived just in time. (Llegó justo a tiempo)
* It's just what I need. (Es justo lo que necesito)
As an adjective meaning "barely" or "almost":
* I just made it to the train. (Casi llego al tren)
* We just missed the bus. (Casi perdimos el autobús)
As part of a phrase:
* Just in case (por si acaso)
* Just for you (solo para ti)
* Just between us (entre nosotros)
To provide more accurate translations, please give me the specific context in which you would like to use the word "just".