I accidentally closed my GIMP toolbox. Can I get it back?
There are two possible solutions I can see:
If the GIMP session is still open, restore the toolbox you just closed by going to Windows -> Recently Closed Docks, and it should be there in the list.
Otherwise, go to Edit -> Preferences in the Window Management section, and press the Reset Saved Window Positions to Default Values button. If you customised either of your palettes (or added new ones), then this method will lose those changes.
To prevent this happening in future, you can uncheck the Save window positions on exit checkbox (same page), so the toolbox always reappears when you restart GIMP, no matter if you closed it earlier or not.
This is what the default dialogs look like:
The main Toolbox is actually quite easy to recreate - it's just the Toolbox dialog (you can create a new one with Ctrl-B or Windows -> New Toolbox if you don't have one), with a Tool Options tab beneath it. Resize the toolbox until a space appears beneath it where you can drop dockable dialogs, then goto Windows -> Dockable Dialogs -> Tool Options, and drag the new dialog's tab into the space.
The other dialog contains four tabs in the top pane: Layers | Channels | Paths | Undo
and three in the bottom pane: Brushes | Patterns | Gradients
Start with the top pane: open the Layers dialog, then open up the Channels/Paths/Undo dialogs (from Windows -> Dockable Dialogs) and drag their tabs in next to the Layers tab.
Then to create the bottom pane, open the Brushes dialog and drag its tab to the very bottom of the dialog window (just above the window border), and the dialog will split into two panes with Brushes at the bottom. Patterns and Gradients can then be opened and dragged into the bottom pane.
Pressing TAB is the toggle for Hide Docks. Which totally removes the toolbox from view. It's very easy to hit on accident. Try this to see if you've hidden your toolbox.