Melyik a helyes mondat vagy mi a különbség?

"ha most tanulok dr a multban 2 evet dolgoztam egy cegnel "

I used to work for a tutorial school for two years.

I worked for a tutorial school for two years from 2012.

Nem kell bonyolítani, elég a sima múlt, csak akkor adj meg hozzá évszámot is.

I used to work for a tutorial school.

I had worked for a tutorial school.

I worked for a tutorial school.

I had worked for a tutorial school for two years. --Perfect kell ha ott van hogy meddig