Even though your infant doesn't know a lick of English, they will get some of the more obvious non-verbal aspects of your communication. The simple fact that mommy is talking happily with them promoting feelings of well-being and safety.
Talking with your infant- as if you want them to understand, in simple clear words - with repetition for memory's sake, primes their still-developing but already-buzzing language centers in their brain to listen, understand, and eventually speak in their upcoming toddler years.
Despite the fact your infant will give little visible feedback - especially in the beginning, that they're listening or understand you, positive genuine verbal interactions with your infant create similar positive emotions in them (as long as they're not too cranky/hungry/need a diaper change).
As a highly social species, language and communication matter so much to we humans' survival, newborns will instinctively mimic the faces of adults in their line of vision.
So don't get too excited when you think your newborn is smiling at you, they're just doing it reflexively (like that adorable finger-grabbing Ulnar grasp) and their mimicking behaviors will disappear by the end of their second week.
Talking or reading to your infant are excellent ways to bond and prime their brain for the task of learning language. These positive mother-directed one-way interactions with your infant will slowly evolve into delightful two-way interactions as they become increasingly social.
After six months the social and communication ball really starts rolling in terms of your infant's eye contact and active listening.
If you're attentive and stay tuned to your child's ever-adapting capacity to understand and speak, by the time your child hits their toddler years, you'll be living with one of the most genuine and hilarious little people you'll ever have the pleasure of knowing.