Juan needs to sleep because he is [tired/sleepy/exhausted].
Let's break down the phrase:
* Juan is a proper noun, referring to a person named Juan.
* necesita means "needs."
* dormir means "to sleep."
* porque means "because."
* está is the present tense of the verb "estar" which means "to be." It is used to describe a state of being, in this case, tiredness.
The missing word after "está" is what specifies the reason for needing to sleep. It could be "cansado" (tired), "soñoliento" (sleepy), "agotado" (exhausted), or something similar.
So, the full sentence could be:
* Juan necesita dormir porque está cansado. (Juan needs to sleep because he is tired.)
* Juan necesita dormir porque está soñoliento. (Juan needs to sleep because he is sleepy.)
* Juan necesita dormir porque está agotado. (Juan needs to sleep because he is exhausted.)