Toolbar
From Space Engineers Wiki
Function
The toolbar serves multiple purposes, the primary being the easy access of materials and components. The toolbar can be hidden by pressing "Tab" at any time, and revealed through the same method. The toolbar has ten slots, the last one being your hands. You can take materials from your inventory at anytime and place them on the toolbar, and subsequently select them by pressing the corresponding number key. (Respectively, from left to right, 1, 2, 3... and so on, until 0.)