You would POST a JSON body with the filter parameters you wish to use.
This blog post covers it in detail. This forum thread also provides examples.
E.g., from the blog, to retrieve records where date > 2012-01-01T00:00:00.000
the included filter payload would be
{"filter": { "date": { "$gt": "2012-01-01T00:00:00.000" } } }