"I am working there now."
Translation:Tha mi ag obair an-sin a-nis.
An is a preposition. It is used with adverbials of time and place - phrases that show when or where something occurs. We do this in English, but we can't agree between us on which to use or even whether to use one.
Tuesday / on Tuesday
on the weekend / at the weekend
Gaelic is actually easier in this situation, because we almost always use an (or variants a, am, depending on what follows), or nothing, to indicate when or where something occurs. Because of irregularities in English, it is translated by on, at, to- or nothing.
an sin 'there'
an seo 'here' a-nis 'now'
an-dràsta 'just now'
am bliadhna 'this year'
an-uiridh 'last year'
Thank you for alerting me to the double nn. I have now corrected it. But notice that whilst you may spell it an-sin, and I did until recent discussions on Duolingo, it is an sin not an-sin.
See https://forum.duolingo.com/comment/36403042?comment_id=39609128 where the official spelling and the lack of logic are discussed.