It can be somewhat tricky to add User Story or another entity into TargetProcess using Ajax and REST API. Here is an example how you can do it using jQuery.

This code creates a new user story in a project with id = 1:

$.ajax({
    type: 'POST',
    url: appHostAndPath+'/api/v1/UserStories',                            
    dataType: 'json',
    processData: false, //otherwise wrong content-type
    contentType: 'application/json',
    data: JSON.stringify({Name:"User Story Name", Project:{Id:1}})
}).done(function( msg ) {
    alert(msg)
});

REST API CRUD Summary Table shows available operations on all entities and additional conditions…

REST CRUD is coming. We are testing it now and will release it very soon. Here are some small samples so far.

REST Create/Update operations can be performed on entity successfully only if entity is well formed (for example, user story is attached to project), in this case response contains created/updated entity…