Some short tips.
This template contains several example pages. Find the ones you need, move them to the top row, remove the rest. You can always rebuild them yourself later from the underlying base elements. If you need to figure out later how certain pages were put together, just clone this template again so you can take a look at the element structures.
Unlike other pages, the root object of your website is a container for the actual home page. Place another page before the inner page element, THEN remove the old one. If you need more hand-holding with this, see the Boomla Component docs.
Note: if you mess it up and don't see the undo button any more, you can always undo it from the Control Panel.
The top menu, the footer, and some page layouts are prepared as components, so you can re-use them and edit them centrally. If you want to edit something but you can't find its settings, it may well be part of a component. Open the component editor to edit those.
You will find a white-on-transparent menu component. When editing it in the component editor, you may want to give it a dark background-color first so you can see what you are editing. Once done, make it transparent again.