When you are married, you have the option of filing as married filing jointly or married filing separately. You are not allowed to file as single.
Married filing jointly means you file one single tax return listing all your combined income, deductions, dependents and credits. MFJ has the lowest overall tax rates and is usually the best way to file. However, by agreeing to file jointly, both spouses are taking full financial responsibility for all the income and taxes, and if there is a problem later, the IRS can come after either spouse, even if the problem was the fault of the other spouse.
Married filing separately means each spouse files a separate tax return reporting only their own income, deductions and taxes. MFS has the highest tax rates and some deductions and credits are reduced or disallowed, especially regarding retirement savings and child care. However, by filing separately, each spouse is only responsible for their own tax return. If spouses want to keep their finances separate, or one spouse is in some kind of financial or tax trouble, separate filing may be needed to keep the other spouse out of trouble.
If you want to file jointly, it is usually best to create a new Turbotax account and start from scratch. It is possible to start with one person's single account and change that to married, but it will only contain that spouse's information and information from the other spouse must be added by hand, it can't be merged automatically.
If you want to file separately, you can keep your separate accounts, but if you use turbotax online, you will pay two separate fees. If you buy the program on a CD or as a download to install on your own Mac or PC, you can prepare both returns from the same program.
