Pages don't appear

I hope someone can help me – I’m a total newbie to WordPress (sorry!) who is helping a friend make changes to a WordPress site that someone else has created, and I’m having some problems.

I’ve created a Page with a gallery using the nextgen plugin, but though I’ve hit publish and the images are showing on the ‘visual’ and ‘text’ views on the admin site, when I go and look at the main website all I get is an error message that says ‘There are currently no posts’. I’ve tried uploading the gallery using both nextgen and the standard ‘gallery’ section on WordPress, but the same error is happening. So I’m thinking it’s something that I’m doing wrong, but I can’t work out what that would be. Is there anyone out there who can help?

The error page is showing up here – https://www.bc55.co.uk/gallery/

Also, once it’s working, can someone tell me how to add the ‘gallery’ link to the header navigation bar on the site which is currently showing the ‘Home’, ‘About’, ‘Services’ and ‘Contact’ tags?

Any help would be gratefully received! Thanks in advance, I hope!

Jennie