Hi gbenj, welcome to Silex!
Grid layout is available in the Display dropdown, but the detailed grid configuration options (grid-template-columns, grid-template-rows, gap, etc.) may not be fully exposed in the UI yet. @ceubri @Jeaan-phi can you confirm?
In the meantime, Flex layout works well and gives you good control over rows/columns — you can set it on a container and use flex-direction, gap, and flex-wrap to organize child elements.
If Grid configuration is something you need, I'd suggest creating a Feature Request post here on the forum so it can be tracked on the roadmap.
If you're new to CSS layouts, this is a good reference for Flexbox: https://css-tricks.com/snippets/css/a-guide-to-flexbox/
Let us know how it goes!