ago = "тому назад" - употребляется ПОСЛЕ слов, обозначающих отрезок времени (типа столько-то минут/часов/месяцев/лет назад)
1 We moved to a big house three years ago.
2 Two days ago my mum got a new job.
3 Six weeks ago Mariya bought a mobile phone .
4 My brother left school two years ago.
5 Half an hour ago I had lunch .
6 We went to the USA six months ago.