Optimizer uses multiple columns statistics if WHERE condition references all columns.
If your query looks like:
WHERE col1 = 1 AND col2 = 2
you can collect stats this way:
1. COLLECT STATISTICS ON table_name COLUMN (col1,col2);
2. COLLECT STATISTICS ON table_name COLUMN (col2,col1);
Sometimes other queries (based on the same table) may reference only col2 in WHERE condition, then option 2 is more advaisable.