Question

what is roster or set builder form?

Answer 1

A set is a collection of objects. Those objects are generally called elements of the set. Set builder notation describes the members of the set without listing them. It is also written between two set brackets. For example,
{x | x is a month that begins with J} .

Answer 2

start off with a left set bracket, then you put x followed by a vertical bar which is interpreted as 'such that'. Then you write out the description of the elements of the set. Finish it with a right set bracket.

Answer 3

If you think of a roster of a sports team, it lists all the members of that team.

Roster form for a set lists all the members of the set

Example {1, 2, 3, 4, 5} This is the roster form for the natural numbers greater than or equal to 1 and less than or equal to 5.

Set builder is a way to describe how to actually build this set.

{x | x is a natural number; 1 <= x <= 5}

This means all the numbers x such that x is a natural number between 1 and 5 inclusive.

Both mean the same thing. Just different ways to say it.