If you are a US citizen and your spouse does not have a Social Security number or an ITIN and you are not applying for an ITIN with the tax return then you can only file your tax return as Married Filing Separately.
The tax return can only be printed and mailed, it cannot be e-filed.
When you print the tax return manually enter NRA for non-resident alien in the block for the spouse's Social Security number.
If you are filing your tax return as Married Filing Jointly you must apply for an ITIN with the tax return and you would need to be providing a statement with your tax return that you want your Nonresident Alien Spouse Treated as a Resident. See IRS Publication 54 Tax Guide for U.S. Citizens and Resident Aliens Abroad pages 6 and 7 - https://www.irs.gov/pub/irs-pdf/p54.pdf
Go to this IRS website for ITIN information - https://www.irs.gov/individuals/international-taxpayers/general-itin-information
