My gallery folder is called "jb-details", and is in with all my site folders in their own folder "APS woodwork".
I'm not sure where the 'jb-main' folder (from both of your sample iframes) comes from.
The 'src' attribute of your iframe should point towards the 'index.html' file within your gallery folder.
The 'src' attribute can be relative (to the web page containing the iframe code) or absolute in the form http://www.example.com/gallery/index.html
For example, if your gallery folder is named 'jb-details' and you have uploaded the entire folder (not just the contents) to the root directory of your web space, then you could use either of the following:
<iframe src=" http://www.apswoodwork.uk/jb-details/index.html" width="800" height="600" frameborder="0" scrolling="no"></iframe>
<iframe src=" /jb-details/index.html" width="800" height="600" frameborder="0" scrolling="no"></iframe>
The leading slash in the second example denotes your root directory.
If you want to use a relative path, then the path will depend on the location of the page containing the iframe code.
Here's another example.
If your gallery folder is named 'jb-details' and you have uploaded the entire folder to another folder named 'APS woodwork' (which is in the root directory of your web space) and you are looking to load the gallery into an iframe in a web page in your root directory, then you could use:
<iframe src=" http://www.apswoodwork.uk/APS woodwork/jb-details/index.html" width="800" height="600" frameborder="0" scrolling="no"></iframe>
<iframe src=" /APS woodword/jb-details/index.html" width="800" height="600" frameborder="0" scrolling="no"></iframe>
<iframe src=" APS woodwork/jb-details/index.html" width="800" height="600" frameborder="0" scrolling="no"></iframe>
I hope this helps.