I am assuming tabs you are referring to are Categories

Go to Edit Post, look for Categories (under Publish) on the right side of screen, check desired boxes, click update in Publish.

Hope this helps

I can't tell without looking at the dashboard side, but I suspect it has to do with how you manipulated the permalink. I would suggest also disabling the supercache plugin, if you haven't already, until you get it sorted out.

It looks to me like the tabs you referred are Pages. If this is the case and you want your first post to be the permanent first page, I would copy and paste it to the Home Page, view it then erase it from post if satisfied to eliminate duplication. I do wonder about why your contact page is showing up twice though. Hope this helps

If you're referring to the navigation, you can add any piece of content from Appearance -> Menu.

That new WordPress default theme seriously bothers me. It's just heavy and weird-looking in this kind of use. I'd pick one of the other default ones if that's the route you want to take.

If you want certain group of posts to apprear under certain tab (it is actually a menu item).
1) Create a category if not already created (e.g. upvc windows)

2) Assign the Post to a particular category when creating the Post.(e.g. upvc windows)

3) Go to Appearance => Menus => Click on category => Select the category (e.g. upvc windows) => and "Add to Menu" (You need to do this once for each tab/menu item)

4) Now, all posts that are assigned to "upvc windows" category will appear under the "upvc windows" tab/menu.

For this to work, your theme should support Menus. Hope this helps.

Hello ! You need to check the you index.php means home page of your wordpress website. Go there and open it where you write the post exclude the category you not want to show there post here. If you done this already then go to admin side and where you publish post unchecked from the Uncategory. Its will be work.

Hello,

I Think This helps you.

Go to Edit Post, look for Categories (under Publish) on the right side of screen, check desired boxes, click update in Publish.

I can help you. Add me to your skype: themubeen