Hi,
1. The layout(Text + Masonry Grid or Grid) is built by BM content builder.
Please read the post how to use the BM content builder: https://doc.seatheme.net/theme/arnold/page-elements-arnold/
How to add a Text module: https://doc.seatheme.net/sea-content-builder-plugin/text-module/
2. The thumbnails of the Grid come from portfolios(featured image), the font is the title of portfolio, you can edit them in Portfolio>All Portfolio, learn more:https://doc.seatheme.net/theme/arnold/portfolio-arnold/creating-a-single-portfolio-arnold/
If you want to config the font style, you need to edit the Grid module, there is font options, learn more: https://doc.seatheme.net/theme/arnold/page-arnold/arnold-grid-portfolio/
3. I am not sure if I understood this question.
To config menu, please read: https://doc.seatheme.net/general-topics/how-to-create-wordpress-menu/
The body text(layout) is built by BM content builder, you edit the page(or portfolio), click BM content builder, you will see the editing panel: https://doc.seatheme.net/theme/arnold/page-elements-arnold/
note: I suggest you read this quick guide firstly, it is a quick guide: https://doc.seatheme.net/theme/arnold/getting-started-arnold/quick-tutorial-for-wordpress-arnold/
Regards!
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