Hello Joao,
Great questions. Let’s find answers for you.
Slides — the slides are edited in the media section of your dashboard. Click on Media there and then choose slides. Each slide will be published there, similar to how a post is published. The featured image of each slide will be the image that is shown.
Menu Group — You can add the new menu group to your front page. It looks like in the home section two of your widgets you’ll be able to find the menu group widget. It has a series of drop down menus that you can use to select the menu groups displayed in the widget. You can use that widget to add the new group to your front page.
You can also add the menu group directly to your navigation menu. That will create a “page” (really a dynamic archive) of all the items published in that menu group.
If you have any questions or trouble, let me know.
Take care,
Bill