To work with a record, you must first select it. Selection can be easily done using the mouse. The selected record is shown highlighted.
Hold down the Ctrl key to select and de-select more than one record. To select multiple continuous records, select the first one with a single click, hold down the Shift key and click the last record. A range of records from the first to last will be selected.
In References module, you can type the first few letters of the first author's last name to select the desired reference. This process is case insensitive. You should not pause for too long between typing each letter.