Create your query in the filters section [A]. There is no need to press enter, as soon as you begin typing or selecting items from the drop-downs, results which match your query will be returned in the results table [B].
Browse the datasets which matched your query using the page browser control located beneath the results table [B].
You may make as many alterations to your query as you wish and the system will continue to retrieve updated results in the results table [B].
Once you find a dataset that interests you, click on the dataset title and you will be taken to the dataset's meta-data page. Please see the View a dataset section for a detailed explanation of the dataset metadata page