Usually, Discriminant Analysis is used to calculate the discriminant functions from observations with known groups. When new observations are made, you can use the discriminant function to predict which group they belong to.
If explanatory variables do not follow a multivariate normal distribution with equal covariance matrices for the level of the response, the use of standard discriminant analysis procedures will be statistically inconsistent. In such cases, logistic regression gives more accurate results.
You can also calculate (choose ) the values of the discriminant function for the observation(s) and then assign it to the group with the highest function value.