You may need to introduce yourself in your English class, or in a job interview, you might need to introduce yourself at a new job, or at a new hobby or leisure activity, you may even need to introduce yourself at a big event or convention in front of thousands of people.
I feel very nervous and anxious when I have to introduce myself to large groups of people, and English is my first language, for learners of English, for my students, this is incredibly intimidating.
Obviously, hello, hello can be both formal and informal, but it's fine to use it in a formal situation, you also have good morning, good afternoon, and good evening, make sure you pay particular attention to what time of day it is.
Now, if you're in a more informal situation, one in which you're introducing yourself to make friends and to meet people and to get to know each other better.