In the dashboard select "layout" from the column on the left [Fig. 1].
You are going to add two widgets. Add the "pages" widget at the top (between the header and blog posts sections). This will become your top tabs. In the sidebar add the "links" widget.
Create the pages for both areas via the pages link on blogger the dashboard [Fig. 2]. Select "show as top tabs" in the drop down menu.
Go back to the layout [Fig. 1] and select "edit" in the lower right corner of the pages widget. Now you need to configure your page list. Under "Pages to show" click the checkbox beside each page that you want to appear in the top tabs.
Under "Page order" drag and drop to sort the pages in the order you wish them to appear in the top tabs section.
For the pages you will use as side links make sure the "Pages to show" box is unchecked so these are hidden. Click "save".
Return to the pages link [Fig. 2]. Here you will now find your pages that show in the top tabs separated from the hidden pages. If you don't see the "hidden pages" group scroll down. You'll find them below the tabs group. Under the hidden page that you want to display as a sidebar link select "view". This will open the page in a new window and you can highlight and copy the URL. For convenience I suggest copying each of the URLs that you will be linking and paste them into a temporary text file so you can add them all to the widget at once.
Return the the layout [Fig. 1], and select the links widget in the sidebar to configure your links list. Give the widget a title and select the sorting method. Paste the URL for the first link in the "New site URL" field. Name the link with the text you want to see in place of the URL. Click "Add Link" Repeat this process until all of your hidden pages have been added to the links list. Click "Save". Your links can be further sorted by using multiple links gadgets with different titles.