Parsing is performed with the use of the nerdamer object which takes a string as it's main parameter.
See the Quick start to get up and running quickly. Note that you can now use internal functions through the new API. For example as an alternative to doing:
you can also do:
var x = nerdamer('diff(sin(x)/x, x)');
var x = nerdamer.diff('sin(x)/x', 'x');