The big brown dog barks loudly.

Meaning: This means a particular dog that is large and brown is making a lot of noise with its voice. It's like saying, That specific dog that is brown and large is making a loud sound with its mouth.

Choice of Words: The is used to refer to a specific thing or person. Big means something is large in size or amount. Brown is a color that is similar to the color of chocolate. Dog is an animal that is commonly kept as a pet. Barks is the sound that a dog makes. Loudly means something is made or done with a lot of noise. When you put them together, "The big brown dog barks loudly" describes a specific large brown dog that is making a lot of noise by barking.