Ó shin plus a length of time means ago and points at a finished moment: cúpla bliain ó shin. Le plus the same phrase means for that long and describes something still true: tá mé anseo le trí bliana. Ó marks a starting point.
Examples
- Cúpla bliain ó shin bhí mé i mo chónaí i mBaile Átha Cliath.
- A few years ago I was living in Dublin.
- Tá mé anseo le trí bliana.
- I have been here for three years.
- Nuair a bhí mé óg, chuaigh mé chuig an trá.
- When I was young, I went to the beach.
The mistake to avoid
Ó shin is finished; le describes something still going on.
Where this fits in
An tAm Atá Thart, Irish Gaelic A2: Talk about the past: yesterday, last weekend, and travel memories.