Beginning documentation on most of these "runic forms" is available through "?".
When used in the Mathematica Front End, there is a blue >> that links to the
main reference page on the item.
In[1]:= ? &
Function[body] or body &
is a pure function. The formal parameters are # (or #1), #2, etc.
Function[x, body] is a pure function with a single formal parameter x.
Function[{x1 , x2 ,
}, body]
is a pure function with a list of formal parameters.
In[2]:= ? /.
expr /. rules applies a rule or list of rules in an attempt to transform each subpart of
an expression expr.
In[3]:= ? /@
Map[f, expr] or f/@expr applies f to each element on the first level in expr.
Map[f, expr, levelspec] applies f to parts of expr specified by levelspec.
