Use most to refer to a quantity of an unspecific group. We use most when we are speaking in general and do not have a specific group of people or things in mind:
Most students ask questions.
All students want A's.
Many students want less homework.
A few students had to stay for a review session. (some)
Few students had to stay for a review session. (not many)
Use most of the X to refer to a quantity of a specific group. Note the expression includes a phrase defining the number to a specific group:
Most of the students in my English class ask questions.
(most - specific to those who are in my English class)
All of the students in my class want A's.
(all - specific to those who are in my class)
Many of the students in my school want less homework.
(many - specific to those who are in my school)
A few of the students who have low grades had to stay for a review session.
(a few - specific to those who have low grades)
Few of the students who have low grades had to stay for a review session.
(few - specific to those who have low grades)
So it means only your first example is correct. But it is correct if for example you write:
Most of the birds which are living in highlands can fly.
About The most I think it refers to the rules of the and there is nothing more.
Most has two closely-related meanings.
1 the largest in number or amount
2 more than half / almost all of somebody/something
As that OALD link says, the most is often used for the first meaning - but informally, the is often omitted. It's never used with the second meaning.
Suppose The Queen of Hearts were to ask "Who ate my tarts?"...
A1: "The knave ate the most"
A2: "The knave ate most"
If several courtiers ate one tart each, but the knave ate two, then either answer could validly be given, since he ate more than anyone else (but note that A1 is a "very slightly formal" usage).
But if the knave actually ate more than half (but not all) of the tarts, only A2 is correct. Though the Queen might not understand that intended distinction, since the could be omitted anyway.
It's worth making the point that the is never included when most simply means very...
"I am most grateful for your help"
...but interestingly, whereas in...
"There were 50 people there, at [the] most"
... the is normally omitted, it's almost always included if we add very as an intensifier...
"There were 50 people there, at the very most"
Best Answer
It does not mean the same thing. Most can be used as a superlative, but it can also be used to indicate that something or someone possesses a property very much instead of the most.
By calling him the most talented writer, the author would exclude the possibility of any other writer being better. That is quite an impossible claim to maintain and will probably only end up in endless and useless discussion!
A most talented writer means roughly the same as an incredibly talented writer.
I think this use of most may be a bit dated... examples I can think of are sentences like: