Dockable Dialogues

 There is space below the toolbox to put dialogues

 To add a dialogue go to Windows > Dockable Dialogues and click on the one you are after

The dialogue should open in the dockable dialogue area automatically if there is already something there. Open one dialogue and place in the space provided, then tabs will open automatically next to it each time you 'Add Tab'. If you want to move it you need to click on the top right black< arrow and you will see a menu where you can detach it then drag it by the tab to where you want it to go.

You will need to keep your tool options open esp. if you do not use keyboard shortcuts. You would be wise to keep your layers dialogue open too.
If you want more than one dialogue open, you can have them on the right side as well - there are some there by default.

If you close them all on the right side you will see this

Here you can open as many dialogue boxes as you want or tabs in one box

Tabs are probably better especially if you work with a lot of layers. Once you fill up the space with tabs you will be given forward/backward arrows to scroll through them.

To add tab to an empty dock you need to drag your dialogue by the tab. If you want to add or remove tabs you will find a menu at the top right of dialogues To add the whole dialogue/window drag it by the top of the window to the space provided.

Close Tab if you don't want the active tab.
Detach tab just removes from the dock
  Use Lock tab to dock so you do not remove the dialogue in error. (It can happen with a simple unintentional move)
Preview size can be changed to whatever size you want some of your things to be (8 sizes from tiny to gigantis preview).  Gradients, Brshes Patterns etc. Not all things will have this and not all tools have options.
Tab style can be changed to just icon or automatic (icon and text)
View as List can be used for things like gradients, patterns, text/fonts, brushes. - they can also be in View as grid. you will be given that option if the dialogue will allow it.
Show button bar' shows a further small menu at the bottom of the dialogue
If you intend to have your dialogues on a different monitor use Move to Screen
Gimp can be used over several monitors