Yes, his power is changing thought into reality via his willpower. When a green lantern uses his power he creates "astral objects" that are a green hue. Now the ring has a limited amount of energy that must be recharged via the lantern. Furthermore the strength of the constructs and what the construct is able to create is limited via the willpower of the green lantern.

Now these green constructs can't affect directly the color yellow. Why this is a limitation has changed throughout the entire series, but if a person is covered completely in yellow he would be immune to a green lantern through direct means. The green lantern can use indirect means to affect him, such as using his ring to drop a heavy object onto the person (and thus the object touches the yellow not his astral hand.

The ring also acts as a universal translator.