Answer to Question 1
Earth's orbit is only very slightly elliptical. Around January 3, Earth is at perihelion, its closest point to the Sun, when it is only 1.7 percent closer than average. Around July 5, Earth is at aphelion, its most distant point from the Sun, when it is only 1.7 percent farther than average.
Answer to Question 2
On the day of the summer solstice in late June, Earth's Northern Hemisphere is inclined toward the Sun, and sunlight shines almost straight down at northern latitudes. At southern latitudes, sunlight strikes the ground at an angle and spreads out. North America has warm weather, and South America has cool weather.