Hi Dapphy,

The usage of 'had' is done in sentences where-in there are 2 depending sentences. Eg.:

"when he had gone to school, the postman arrived."

which says that postman arrived when he was not available. We cant say - the postman had arrived, when he went to school. THis will give a totally different meaning.
So take it as a rule, chose 'had' only when there are 2 depending sents.

Else in other cases has is used. like:
"He has gone to school".

We cant use had in above case alone. we can only used it when we say it with some other depending sentence.

I hope it has not confusd you even more.

Do let me know !!

I get it, that makes sense, I'll think of this when I do my SC problems in the future!