OK so the Blog if that is a separate Page then you would use the full URL, just add the menu itme from the list. All other onpage links would just require the # href.
How are you creating the Sections? If it is the GP Sections then on the settings tab of the section there is an ID field.
If its a pagebuilder – eg. Elementor then each Section > Advance settings also provides an ID field.
If its the block editor then again the Settings Sidebar > Advanced will have an ID field on certain blocks, like the heading block.