Before they start to make actual words, children love to make baby talk. What is often just a slew of sounds put together as gibberish is actually a very important part of their development process. During this time, babies are learning the full breath of the sounds that are possible to make with their mouth. They are also learning how sounds fit together, which is the precursor to forming sentences and complete thoughts.
The child in this video is just at the age where she is starting to become more comfortable with speaking. She mimics and follows sound patters that she hears, but without actual words, the sentences can sound quite strange.