I think you need to work on some understanding of what exactly "vector" is - once you get your head round that, then everything else makes much more sense and you could probably work the rest out yourself:
A "Vector" image is one that is made up of points and lines connecting them. If these lines close, then the shape inside can be filled. Each set of lines (objects) exist independent of each other - one can be above or below another.
Each point on a line or object (node) defines the direction of the line coming into it and going out from it. This can be changed by using the "shape" or "node-edit" tool. You can also use this tool to drag the line into a new position; this changes the directional information from the nodes at either end that are used to create the line.
A line can have just about as many node points on it as you want. If the start and end points on a line join, then it becomes a closed shape that can be filled (Although there is a button to automatically create an 'invisible' line that joins start and end points so it acts like a "closed shape")
Multiple lines, objects and shapes can be flattened together in one of three ways:
- Combining. They become the one object, sharing a common fill and common line properties. Node-editing allows you to shape all the nodes on this object. Every 'closed' shape is filled, so that if you have two (filled) overlapping circles, the overlap area will not have a fill.
- Welding. Very similar to combining, but overlapping lines and shapes are discarded. In the example above you would end up with a completely filled eight shape. There are many weld tools to trim, weld, create shapes from overlapping areas and otherwise use two objects to create another one.
- Grouping. This just lumps all the selected shapes together - each maintains it's original property and relative position in the layers of objects. But you can move, stretch and scale as one object, and any fills or outlines applied to the group will affect everything within it.
Since you are normally working with lots of objects, the order of them on the page is quite important; here the "object manager" comes in handy. With this (and short-cut keys, and the "arrange" menu) you can make sure that text is infront of an image or bits of an image are hidden by other bits. Each piece/colour/object in your final image does not have to butt against another - the one above can overlap the one below.
And that's about it. Once you understand the way it works, all the tools, effects, shapes and fancy stuff is just bells and whistles to make it easier for you to produce the final result you're looking for.
(BTW - back to the initial point: it's all coordinates and joining lines. You can scale these up or down with no loss of quality.)
Hope this is of some use
~Gadget~