The flu primarily spreads through respiratory droplets propelled into the air by sick people from coughing, sneezing, or even talking. The flu can also be spread through saliva. More rarely but still possible, people can tough and pick up virus on surfaces and infect themselves by touching their mouth or eyes.
Reference:
Harvard: health.harvard.edu/staying-healthy/how-long-does-the-flu-last#:~:text=Symptoms%20usually%20appear%20from%20one,may%20continue%20to%20feel%20fatigued.