This is where you can manage the custom fields. Use the top right toolbar to add / modify / delete / publish / unpublish fields. All these buttons ( except "Add new" ) can be used only after at least one field is selected from the field list.
You can select one or more records by clicking on the checkbox on the first column of the table. Click the top checkbox to select all the records on this page.
On top of the table you have some tools that will help you filter the fields. Enter a partial/entire name of the field and click "Go" to filter the fields. Click "Reset" to remove the filter.
Click on the name of each column of the table to order the records by that column. Click a second time to order the records in revers order. Click "Reset" to cancel the ordering.