Learn Romanian: Băiatul e acolo.

Băiat means 'boy', while băiatul means 'the boy'. Unlike English, Romanian attaches the word for 'the' (the definite article) to the end of the noun. For most masculine singular nouns ending in a consonant like băiat, you just add -ul.

Why does the sentence use e instead of este for 'is'?

E is a shorter, very common version of este. Both mean 'is' and are completely interchangeable in everyday spoken Romanian.

Could I just say E acolo without using a subject?

Yes! If it is already clear who you are talking about, you can drop băiatul and simply say E acolo (He is there). Because the verb e tells us it is a third-person subject, Romanian often drops the subject pronoun entirely.

Does acolo mean 'here' or 'there'?

Acolo means 'there', referring to a place further away from you. If the boy were standing right next to you, you would use aici (here) and say Băiatul e aici.