I suspect that given the nature of these websites this will be a popular tab! So I will try to give a good help page.
To add a gallery to your website you will need to use this to make it, create a page to display it, add the page to a menu, and upload files, so effectively a combination of every help page here.

If you click Gallery Options you will see a screen like the picture below, each Gallery MUST have a title and by default this will also be the name of the gallery.
The Type drop-down list gives options on how the gallery is displayed this will be seen when you go into your gallery, BUT there is a difference between devices so a PC may work differently to a phone

Maximum thumbnail and Image dimensions will affect how the screen appears, if left blank defaults will be used which are fine if you don't have too many pictures in the gallery defaults are fine, if your gallery grows then you may want to experiment.

Clicking Add Files links back to the pictures you have uploaded, hence the reason to organise and name them well When your file is chosen there are 3 boxes for text first is the short title last is the description not yet found out what the middle one does.
Finally click the Save gallery button to save it!
The line of code in the demo case (% gallery name=demo %) shown in the picture is what you need to copy into the SOURCE option of a web page have a look at the demo gallery page to see how it is used. that is the only line needed, but you can use the page editor to add a title or any text you want to the gallery pages.
Help pages for Woodturners.UK websites using GetSimple
written by Pete Ravenscroft 2021