The help is inaccurate. LibreOffice does not use a real baseline grid but a reference paragraph style. In InDesign you would set the grid line distance, whereas in LibreOffice you specify a body text paragraph style. Imagine a full text page with this style applied. This looks as if there is an invisible grid to which this lines are aligned. So you set the ‘grid’-line distance indirectly by the row height of the reference paragraph style.
The base setting is in the dialog page “Page” of the page style dialog. Check the box “Register-true” and then enter the reference style. If your body text has the style “Text Body”, then you need to select it there. This is a setting per page style, so if you use several page styles, you have to make the settings several times.
You can then decide for each paragraph style, whether the lines of the paragraph should snap to the ‘grid’ or not. You find this setting in the dialog page “Indents & Spacing” of the paragraph style dialog. For the paragraph style “Text Body” it should be enabled. But for the paragraph style “Quotations” is should be disabled, because for a block quotation it is usual to use a line spacing with reduced leading and that would be overwritten by snapping to the ‘grid’ induced by the style “Text Body”.
You can easily test your settings, if you temporarily set the page layout to two columns. The lines in the columns should be vertically on the same positions.