Two good starting places,

   http://reference.wolfram.com/mathematica/tutorial/GettingUsedToMathematica.html

   http://reference.wolfram.com/mathematica/tutorial/GettingStartedOverview.html

They are also in the Mathematica (Help menu) Documentation Center as
  
   tutorial/GettingUsedToMathematica 
   tutorial/GettingStartedOverview 


In some cases in which you don't know the right names or syntax, you can ask the Wolfram|Alpha web
site to guess what you mean and send it back to Mathematica. Type an "=" sign before the input or click
"Free-form input" from the horizontal insertion line. Note that the Wolfram-Language input is included
in what comes back.

Mathematica does not plot it because it is not written in Wolfram language. Function names begin in capitals and must be correct. Square brackets are used for arguments. There should be no space between the function name and the bracket. It all needs to be quite precise.