If I am doing a two tailed $t$ test, i.e my null and alternate hypothesis are
$$H_0: \mu = 0$$ $$H_1: \mu \neq 0,$$
then would I choose and $\alpha$ value of $0.05$ for a $95$% confidence interval or a value of $0.025$?
EDIT: Also, will be degrees of freedom be $n - 2$ or $n - 1$?