llc

Is it is a single member LLC?   If so, you will enter the tax ID for your LLC on Schedule C.   Use your social security number when starting your return in the personal information section.   Then, when you get to your self-employment income and expenses, you will complete a Schedule C.   You will be asked if you have a separate tax ID and name for your business.   You will answer Yes here and enter your LLC's tax ID.    The screen you enter it on will look like the one below.  

If your LLC is a multi-member LLC, you can't use the personal TurboTax products; you will need TurboTax Business for your LLC return.  A single member LLC is a disregarded entity and can be included with your personal tax return.