To start Mathematica with the X Front End type:

tap mathematica; mathematica

If you want to start Mathematica without the X Front End type:

tap mathematica; math

Once it's started an empty 'notebook' appears, and you can typing your equations
in this notebook.  Each piece of information in the notebook is contained in a
separate cell.  A cell can contain text (in form of equations), input and output
, or graphics, but not a combination of these.  The cells can be cut, pasted,
copied, and printed, by themselves.