I have a trial balance for Dec 31, 2011.
...
Unearned sales revenue 4 000
Cost of goods sold 171 225
Sales 263 770
...

I need to prepare an adj. entry:
Unearned sales revenue of $975 is still unearned at Dec. 31, 2011. On the sales that were earned, cost of goods sold was $2 000.

So I did the following adj. entry:

1) Unearned sales revenue 3025
Sales revenue 3025

2) Cost of goods sold ?
Sales revenue ?

I am confused, don't know what exactly and how to do the entries.

Number 1 is correct

For number 2 your credit should be to finished goods inventory or merchandise inventory (whichever inventory account you have).

So, it would be
Cost of goods sold 2000
Merchandise inventory 2000
The amount would be 2000, like it was given in data for adjusting entry?

You are correct.

Thank you very much!!