For the second part. That state is a ‘text’ format type. Then we set the State to a specific text when certain buttons are clicked, such as home. And use Conditions on the groups to show or hide when the corresponding text is an exact match.
For the first part, it is a few more steps to do a previous page. You will need to create a new state, such as 'Previous Page (type=text). And then you can save the text of the previous group when you navigate to a new one.
When the ‘Back’ button would be clicked you would need to set the state as ‘Index’s Previous Page’ (text)
If you still need assistance with this concept, please create another forum post or find a previous one that is relevant to the topic of ‘previous page’, to keep this one template specific needs/bugs 