hi ..pls help me

[chela]

hi there
Please differentiate these 2 sentences and please explain it .

1. I [was to] buy the train ticket.
2. I [was to have ] bought the train ticket .

shall be very thankful.

[Lucretia]

Hello Chela,
#1 means according to some arrangement or plan you had to buy the ticket. It's not clear whether you did or not.
#2 means you had to, but you didn't buy the ticket.

[eeshan]

I buy the train ticket.
It is something you have done previously and now, you are describing it to the third person.
Eg. I go to the Train station, I buy the ticket and then I start walking towards the lounge..........

I bought the train ticket. Past tense.
You have already done so.......
The basic difference is that the first sentence is an incomplete one and is used in continuation of a conversation taking place.
Second sentence is complete.
Regards