I want to know about the different Lokas in this universe & also description of Golaka Vrindavan.

Can you explain it to me or you can provide links about them?

If You can here download some flash books:

http://ebooks.iskcondesiretree.info/index.php?q=f&f=%2Fflash%2F01_-_Bhaktivedanta_book_trust_books

and also better if You read Bhagavad Gita - As It Is with the purports of Srila Prabhupada. You can find it here:

http://ebooks.iskcondesiretree.info/index.php?q=f&f=%2Fpdf%2F00_-_Srila_Prabhupada

When we have knowledge we become strong. And only than we can help others to become happy.

Knowledge is like a sword which cuts all covering of ignorance from our soul and we will be able to the truth. Because Krishna's body is full of knowledge, bliss and eternity. And we are His particles. In this way in the reality we have all knowledge but for this time it is covered with this ignorance of material body.

Also please find out lectures about Spiritual World here:

http://audio.iskcondesiretree.info/index.php?q=f&f=%2F02_-_ISKCON_Swamis%2FISKCON_Swamis_-_R_to_Y%2FHis_Holiness_Radhanath_Swami%2FLectures%2F01_-_Theme_wise%2FSpiritual_world