If you are a Single Member LLC as an S Corp you need to file a separate 1120 S Business return. You should do the S Corp return first since you get a K-1 or W2 from the S Corp to enter into your personal return.
If you are not a Single Member LLC filing a S Corp return then it is a disregarded entity and you file it on Schedule C in your personal return. Disregarded Entity means you dont file a separate Business return. You file it as personal self employment on Schedule C.
