Cant figure this out for the life of me!

[kobelka]

Hi all,
I have a Nikon d5100 dslr that I cant figure out!
It takes great pictures of my kids, family, dogs and everything I want it to..... Except when it comes to my tank.
I have read the manual and watched and read on the net on how to set the custom white balance but cant get it. Also I cant figure out how to take a pic without the flash?
I see the pics that many of you post and am in awe.
Any tips?
Anyone familiar with this camera?
Thanks
Dave