In Mormonism, "agency" means the ability to choose between right and wrong. Just like when you pick out what toy you want to play with - you get to make choices in life.
Mormons believe that God gave people this ability to make choices so they can learn and grow. They think it's important for people to use their agency to make good choices and follow God's commandments.
But sometimes people make bad choices, and that's where consequences come in. Just like if you decided to play with scissors and accidentally cut yourself - actions have consequences. Mormons believe that bad choices can lead to negative consequences, but that God also offers forgiveness and ways to make things right if you mess up.
Overall, agency is about having the ability to choose and learning from the consequences of those choices. It's an important part of Mormon beliefs, like learning from choices you make while growing up.