How to setup GALLERY ?
1. Create as many gallery items ( Gallery -> Add Gallery Item ) as needed. Each gallery item is one thumb on gallery page.
2. For each gallery item set FEATURED IMAGE which will be used as thumb on gallery page and check other options such as size or what will happen when user clicks on thumb - video, image, gallery popup etc... and add proper category to each thumb if neede e.g landscapes, people etc...
3. Create new page called e.g Gallery and use page builder to add Gallery module to it. Choose display options by clicking edit ( green button in top right corner of gallery module ) and categories to fetch - e.g You can display all gallery images by selecting "All Items" or just certain categories - e.g landscape, people etc... - this technique allows You to create unlimited separate pages with different galleries.
4. Choose page layout - sidebar etc... add text above/below via pagebuilder and publish page.