When do we use "das" and "es" and what is the difference? For example:
Das kann ich machen.
Es kann ich machen.
Das habe ich ihm gesagt.
Es habe ich ihm gesagt.
"Das" (this) is a stronger statement than "es" (it). So you use "das" in the first position for emphasis. You would use, "es," if at all, in the third position or later.
You would not say Es kann ich machen, because its placement in the first positon (for emphasis) is incongruous with its weakness, but you might say Ich kann es machen.
The difference between es and das is, that das is a demonstrative pronoun here and es just a normal personal pronoun (in the accusative).
Your sentences starting with das are perfectly fine. You used a demonstrative pronoun, because you want to stress it and can therefore also put it at the beginning of the sentence.
Your sentences starting with es, however, sound odd. I’m not sure whether they are really grammatically wrong, but saying that will raise a few eyebrows. You would normally say "Ich kann es machen." or use a demonstrative pronoun straight away as you did. To sum it up: You just don’t say that.
(In Liechtenstein people speak like that, although it can be considered part of their dialect as you normally never hear people in Liechtenstein speak standard German.)
Compare another gender, e.g. der Mann.
Den habe ich euch beschrieben
it would never be "Er" in that case, because this object is Akkusativ. As for position, I would say either
Ich habe euch den beschrieben
Ich habe ihn euch beschrieben
which is somewhat confusing. I can't explain that.
With neutral gender the same sentence would be:
Das habe ich euch beschrieben
Ich habe euch das beschrieben
Ich habe es euch beschrieben
Er/Es wurde euch beschrieben.
That smells like raising (which I just recently heard for the first time and don't fully understand or believe yet; I don't think German grammarians use that concept, but I don't really know).
Therefore, the deciding difference is that "Es" in the first position wants to be the subject.
PS: If in doubt, just speak with contraction: "Ich kann's machen". That may be why both "das" and "es" work in that position, or why people say "Ich weiß' nicht" (instead of "ich weiß es nicht").