The rack holds all tiles for one move, as in the normal game. Tiles are arranged automatically, if it not fit on one line the rack's heights is adjusted appropriately. The rack can be placed on right top above the messages or left bottom below the 2D view (rack position) and hide its header (vis context menu on right click).
Every player is provided with as many tiles as in the configuration specified. Classic games are run with seven tiles but you can have as well more or less.
Tiles are placed per drag 'n drop from the rack onto the board, that is the 2D view. But you can re-order tiles on the rack per drag 'n drop as well. Either you exchange the position or you 'squeeze' it between others. The operation that is being performed is fed back with the cursor decoration that changes to a 'ying-yang' symbol or an arrow to the left or right. Additionally, you can scramble the tiles: the function is available per context menu when you right click the rack's header.
Per right click a tile on the rack it is marked for exchange and grayed out. You can mark as many tiles as you want to exchange. If you right click it again the status is toggled to normal. You cannot mark letters when a tile has been placed on the board - and you cannot place a letter when something is marked. The marked tiles will be exchanged when you finish your move by calling the next player, e.g. per toolbar button.
In the 'what-if' variant one tile on the rack can be converted into a joker (jokerization). To do so right click it with pressed ctrl key. If the feature is not available at all, a warning is shown.