Question

explain how the size of Ka value shows how far the acid is dissociated into ions

Answer 1

we can see why the Ka value tells us how far the dissociation of acid has progressed into ions by thinking about what Ka is really defined as.
Ka = [H+][A-]/[HA]
as the acid (HA) dissociates into its ions (H+ and A-) the top of the equation gets larger and the bottom gets smaller, so Ka gets larger.
Therefore we can conclude that the large the Ka value for an acid the greater its ionized.
A similar argument can be followed to see why Kb tells us how much a base has formed its ions.