Step 1: Read the question.
We must state the main purpose of vocational information.
Step 2: Define vocational information.
It is factual knowledge about careers, including skills, qualifications, and growth prospects.
Step 3: Test option A.
Preparing only for exams is purely academic and ignores career awareness, so it is wrong.
Step 4: Test option C.
Promoting sports is unrelated to occupational knowledge, so it is wrong.
Step 5: Test option D.
Financial assistance is a support scheme, not information, so it is wrong.
Step 6: Confirm option B.
Providing information about different occupations exactly matches the aim of vocational information.
Step 7: Conclude.
Hence its main purpose is to inform about occupations.
\[ \boxed{\text{B. To provide information about different occupations}} \]