Publishing a new Page results in it showing multiple times on Nav Bar

Hi,
I am new to WP, picking up admin of our website from previous people. While I think I understand the basics of the structure and management of posts and pages, I am not very good in understanding how to control the Theme and it’s associated php files.

That said…
I am admin for the following site:
https://www.RBSTheatreCompany.co.uk
WP uses a theme called “smoothgroove”.
I am trying to add a new page which will show on the Nav bar on the left. I have written the page, but when I published it it resulted in the page showing multiple times on the Nav Bar.
The theme does not “natively” supporting the Menu so I enabled it using Appearance – Menus. But whatever changes I have done there it seems that the categories/pages are managed via one of the Theme’s templates, which I dread touching.

I am not sure to control the Nav Bar entries. Here is what I find looking at these entries in the Nav Bar when I look them up in our dashboard:
1. About the Theatre Company – this is a page. It is not linked to any category, with (NO PARENT) and 0 order. So how does it make its way to the Nav Bar?
2. Meet the Committee – this page appears twice in the Page page – both entries hold the same permalink (id=18). They are not copies, but the same entry – just showing twice (if I make the page in one instance as Draft – it does the same in the other entry -= making me think that if I delete one the other would be deleted as well; so it seems like a WP bug). It is also without a parent, 0 order.
3. Past Productions – a category, not a page. This part seems to be controlled properly via the Categories & Posts option.
4. Upcoming Productions – a category, working fine.
5. Social Events – a category, working fine.
6. How to join – this is a page, and again, unclear how it makes its way to the Nav Bar.

I tried to create a page “Tickets for our show” which I wanted to have at the bottom of the Nav Bar. When I published it it appeared multiple times in the Nav Bar, sometimes 3 times, sometimes 5 or 6 times. It was consistent for that session but if I played around with it and published again I think the number of times it appeared changed, but I am not sure on that.

So…
I need help in:
a. identifying how Nav Bar entries 1,2, and 5 made their way as Pages into the Nav Bar
b. should I worry about that double entry of Meet the Committee? Is that a WP bug?
c. How do I chnage the order of the Nav Bar entries not to be sorted alphabetically (as it seems at the moment; How to Join page is an exception to this – and again I do not know how this is controlled and why the latter is an exception)
d. Most importantly – how do I publish the Tickets for Our Shows page as an entry in the Nav without it showing multiple times?

The Smoothgroove theme php sheets must have been adulterated. I see also a few widget php sheets under the template editor page. The entries there are:

Templates
* Archives – (archive.php)
* Footer – (footer.php)
* Header – (header.php)
* Main Index Template – (index.php)
* Page Template – (page.php)
* Search Results – (search.php)
* Sidebar – (sidebar.php)
* Single Post – (single.php)
* Theme Functions – (functions.php)
* cat-posts.php – (cat-posts.php)
* category-9.php – (category-9.php)
* content_extract.php – (content_extract.php)
* dd-lastest-from-each.php – (dd-lastest-from-each.php)
* dd-list-subpages.php – (dd-list-subpages.php)
* flexi-pages-widget.php – (flexi-pages-widget.php)
* flickr-widget.php – (flickr-widget.php)
* flickrrss_widget.php – (flickrrss_widget.php)
* fold-category-list.php – (fold-category-list.php)
* fold_page_list.php – (fold_page_list.php)
* get-a-post.php – (get-a-post.php)
* intro.php – (intro.php)
* intro2.php – (intro2.php)
* page-links-to.php – (page-links-to.php)
* relatedcategory.php – (relatedcategory.php)
* the-excerpt-reloaded.php – (the-excerpt-reloaded.php)

Styles
* Stylesheet – (style.css)

I am using Firefox on Windows7, if that is of any importance.
A huge thank you to anyone that is able to decipher these mysteries for us…!
Eroka