On the Add Players dialog, press Ctrl+F to open the Find section. Check the "Auto perform action" checkbox. Now, when you search for a player (by name, ID, whatever), and the results of that search are a single player only, they'll automatically be bought in. This enables being able to buy a player into the tournament by simply scanning an ID card.
On the Preferences tab, in the Behavior category, about 20 checkboxes down you'll find "Automatically search as soon as text is entered". This shows/hides the "Find" button so that a search will occur only when the Find button is pressed, or when any text is entered.