If you want a completely empty home page, I suggest using the custom pages plugin and pointing your home page setting in the ACP to a blank custom page.
Otherwise, you can use css
I'm new to nodeBB. the new topic button doesn't do anything. do i need to add a plugin for it to work ?
You might need to activate one of the composers. The default composer should be activated, but perhaps it got deactivated by you? Give that a check.