bump on my penis

Sir i have bump on my penis. It is a big and white bump. Please tell me what i do. 

Possibly a harmless cyst? Best to have it checked by a doctor. If you have photos it would help, but you have to use a computer.

It's hard to offer advice without seeing a pic.  You need to be on a PC or laptop with a large window to add pictures.  If you are, then you should see some extra icons towards the top right of where you type, and the right hand icon (which I think is supposed to look like the sun over hills) will add images.

The pic I've attached here shows the icons.

How long has the bump been there though?