How do I enter income that is not included on a W-2? I received 3 payments from Long term & short term disability payments, but only one check was included on the W-2.

Not all disability payments are taxable income.  If the premiums for the policy that paid your benefits were paid by you, with after tax funds, then the benefits are not taxable.  If your employer paid the premiums, or you paid with pre-tax dollars, then the benefits are taxable.  If you believe the other payments were taxable, you should contact the employer or insurance company to get the appropriate tax reporting form showing FICA tax withheld.  If you want to just add it to your tax return:

To report "employee compensation" income on your tax return:

• Log in to your account and go to your return
• Click on Federal
  
• Wages & Income
• I'll choose what I work on 
  
• scroll to Less Common Income
  
• select Start (or Update) for Miscellaneous Income
• Select "Other income not already reported on a Form W-2 or Form 1099"
• Click through till you get to "Employee compensation that was not reported on a W-2"