A chicken can live alone and they'll be okay.
You can have just one chicken and have it live alone without other chickens or roosters around it.
However chickens get pretty lonely when they are alone and not around other chickens so it's best to have at least 2 chickens instead of just one chicken.
Having a second chicken will keep the one chicken from becoming lonely.
If you want the chicken to be happy and eat correctly and not starve itself to death the chickens must have other chickens around it so that the chicken feels calm, safe and secure.
But if you just want one chicken for now it's okay but I would recommend getting a second chicken to keep the first chicken company.