formula to calc outstanding balance

Hi all,
I am hoping some kind person can help me!

I am a rank amateur at excel and need a lot of help setting up a spread sheet that I am marking to record my savings for a new bike!
l thought that I know the formulas but am having trouble.
The spread sheet that I am trying to mark is set up, like this;

Row A- Date
Row B- Amount
Row C- Amount to saved
Row D- Amount to save

Want I am trying to do is, have column B added to column C.
I thought this formula =b2+c2 would work but no luck.
And I want the column D to show the Amount I still have to, Total cost to save $2,300

Any help that could be offered would be awesome! Thanks