However, even when you master these techniques you'll find that your drawing needs some modifications. Your emblem is a complicated stack of many shapes so adding outlines and changing colours is not straightforward. For example, the rings in the sun pattern are a sub-group of four filled circles. The spokes are six separate shapes. Each of those has two sub-paths. The sub-paths are not perfectly aligned (or overlapping) so the union operation can't join them. You need to combine all of these into a single seamless shape. Some node editing is needed, or it may be simpler to redraw some items. There are similar issues with the ocean, the shield and the crossed "N".
Beginners' Questions Conver color svg label into black/white version
Inkscape.org
All this is possible, but you'll need some practice with [Path > Stroke to Path] and boolean operations.
The path tools have been extended and improved since the manual was written but the information is still valid.
[Help > Inkscape Manual]
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Paths-Creating.html#Paths-From-Conversion
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/Paths-Combining.html
Another useful tool is the Shape Builder [x], recently added to Inkscape.
https://inkscape.org/doc/release_notes/1.3/Inkscape_1.3.html#Shape_Builder_Tool
However, even when you master these techniques you'll find that your drawing needs some modifications. Your emblem is a complicated stack of many shapes so adding outlines and changing colours is not straightforward. For example, the rings in the sun pattern are a sub-group of four filled circles. The spokes are six separate shapes. Each of those has two sub-paths. The sub-paths are not perfectly aligned (or overlapping) so the union operation can't join them. You need to combine all of these into a single seamless shape. Some node editing is needed, or it may be simpler to redraw some items. There are similar issues with the ocean, the shield and the crossed "N".