Social Security mails out SSA1099 to you in January. If your ONLY income is Social Security you do not have to file a tax return unless you have a 1095A for marketplace health insurance. If you had other income in addition to the SS, then you may need to file a tax return.
Go to Federal> Wages & Income>>Retirement Plans and Social Security (SSA1099 and 1099RRB) to enter your SSA1099.
If you did not receive your SSA1099
Go to www.ssa.gov You have to create an account with a user name and password.
https://www.ssa.gov/myaccount/replacement-SSA-1099.html
https://www.ssa.gov/onlineservices/
https://www.ssa.gov/myaccount/
Who has to file?
http://www.irs.gov/uac/Do-I-Need-to-File-a-Tax-Return%3F