All spelling and grammar checking options are here. You can select the dictionary to use for you language, the file that collects words that you 'add' whilst spell checking. (Your custom dictionary) and gives several options to ignore spelling errors in certain cases. You can also access the 'Auto Correct' options from here by pressing the button.

The right-hand side of the dialog is only enabled with certain language selections and set rules for those particular languages.

In the main, you should not need to make changes here as they are picked up from Window's language settings, but is nice to have the ability to switch if you are working in more than one language.