Indicates that something happens or is done after a certain point in time, often with a sense of 'subsequently' or 'later on'. Commonly used in both spoken and written Japanese.
I'll contact you later.
I found out later that he had been lying.
I realized later that I had left my umbrella behind.
She said she'd come later.
Let's work hard now so we don't regret it later.
The package will arrive later.
後から means 'afterwards' or 'later,' whereas 先に means 'beforehand' or 'ahead of time.'
Compound of 後 (あと, 'after') and the particle から ('from'), literally 'from after'. The adverbial use developed naturally from this combination.