I have posted questions here which are unrelated to avoid creating four posts (I know this method is debatable).

If I create a line (freehand) and would like change its profile, remove kinks, etc, how can I do this?

If I select a selection of an image and click any of the snappings (right of screen), nothing seems to happen. How can I see the functionality of the snapping mmodes?

If I have an mage with, say, black in it, and I would lime to change a selection of the balck to another colour, how can I do this without changing all the balck?

Regaring the grid, can this be sized and moved, or must it be use as is?

All is covered here:
http://tavmjong.free.fr/INKSCAPE/MANUAL/html/index.html

and:
viewtopic.php?f=5&t=745#goto-screwedup

Freehand made tools don't preserve your movements and apply the smoothing as an lpe, so the only setting you can make is before the use,
about the smoothing amount (I usually use about 37%). The spiro effect and the pattern along path can be removed later though with the path effect editor.

Snapping is only present if you move one part of your image towards another.
It won't automagically snap objects or parts of them together if you are not in an active transformation.
There is the pixelsnap extension that might help for that.

Your next question I cannot understand.

The grid can be set up in the document's properties (Shift+Ctrl+D).
You can adjust different origo of it, and different divisions.

Lazur URH wrote:Freehand made tools don't preserve your movements and apply the smoothing as an lpe, so the only setting you can make is before the use,
about the smoothing amount (I usually use about 37%). The spiro effect and the pattern along path can be removed later though with the path effect editor.

Snapping is only present if you move one part of your image towards another.
It won't automagically snap objects or parts of them together if you are not in an active transformation.
There is the pixelsnap extension that might help for that.

Your next question I cannot understand.

The grid can be set up in the document's properties (Shift+Ctrl+D).
You can adjust different origo of it, and different divisions.

Thank you for responding.

I didn't realise that Freehand could not be edited.

I now have a better understanding of snap, I thought that it meant snap to grid.

You are quite right regarding the grid which can be set. I suppose that the difficulty is deciding what dimensions to set at the outset - maybe trial and error. However, there are defaults.

Regarding the question you did not uderstand. I will attempt a re-phrase.

Supose I have an image that is composed of a number of objects containg the colour black. The object are connected. When I tried to bucket fill one of the objects (activated for editing), all the balck colour changed (throught the total image). So I wondered if I could isololate an aspect ot the image so that other aspects would not be affected. I thought that highlighting for editing would be sufficient. I will try this again.

Best wishes. You answers have been helpful

The freehand tool makes also a path, just as the pen tool, thought you asked about that kind of kinks -to be able to edit how the shape looks, no matter the "core". It can be edited just the same as any other paths, made with the pen tool too.
Actually there is a sketch live path effect that can vary the shape on a path through setting some parameters.

With the black colouring, you may try to traw a rectangle over the right area, for example with a red fill and 50% opacity, so that other parts won't get registered with the right threshol setting.
Usually the bucket fill won't produce a clean result, as it is based on the image rendered on screen, and not on the vectors.

Filling can be adjusted in the fill and stroke panel (Shift+Ctrl+F), and it's a common solution to have different objects for the outlines and the fills -one path with no outline set but fill, and a duplicant (Ctrl+Shift+D) over it with no fill but stoke.

All the best!