Click a letter in the index at the top of the page to filter terms in the left sidebar and the main view below the index to those that begin with that letter.
Type something into the left sidebar Filter to filter terms in the sidebar to only those that contain the text you typed. This filters terms from the currently selected index (letter) or all terms if no index has been selected.
Click a term in the left sidebar to display just that term in the main view. There may be duplicates from multiple vocabularies.