How do we know the atmosoheric composition, size, temperature, etc. of millions of other planets farther away from Earth?

When we look through a Kepler telescope. The size is determined by looking at the amount of light that passes through the front of a planetary star.
It calculates the year by looking at the time differences that pass through it
Then the atmospheres can be understood by looking at the spectrum of a planet as it moves closer to a star
And when the planet rotates, the star will move slightly because of the gravitational pull. We can find the mass by looking at it.