How can I file tax in US if I've moved out to another country?

It doesn't matter where you stay. You have to file income tax returns and gift tax returns even when you have moved to Germany and Europe. You can file your income tax return online through the EFTPS (Electronic Federal Tax Payment System). To take advantage of this, you have to register online first. Once the registration is complete, you have to wait for 10 business days for a letter containing all the details required to file your income tax return online.

Yes, you need to file the tax. Talk to a tax consultant for it.

You have to file taxes, it doesn't matter wherever you live. You can file your income tax return online through the EFTPS (Electronic Federal Tax Payment System). You can do it by making registration online.