Set the Undo times to decide how many actions you can Undo/Redo. The maximum is 180. Higher values require more system resource.
The temp folder is a folder for temporary files created by iClone during usage. You can define where temporary files are saved in the preferences settings.
Click the Choose 
button in the Temp Folder option and browse to a folder you wish to use as the temp folder.
Make sure the hard disk the temp folder is located on has sufficient free space especially when you are using iClone to produce high resolution videos.
The texture editor is an image editor you frequently use. It is used to show the UV reference map for creating custom texture images.
The Scene Mode drop down list determines if the floor is shown or hidden when you create a new project or applied a new character.