I have never worked in the US, however I am a full time college student. In the summer of 2019 I had a three months internship back in my home country Kazakhstan. They paid in cash and didn’t pro

[JohnB5677]

If you are a Kazakhstan citizen and you didn't work while in the United States, you will not have to file a US income tax return.

[kamtyox]

I am a US citizen 

[DeanM15]

If you are a US citizen you are generally required to file a return based on your worldwide income. 

If you made money in a foreign country it is generally taxable. You can see here if you made enough to require filing. If you were working for three months it seems likely that you do have a filing requirement. 

If you paid taxes on the foreign income you can get a credit for foreign taxes paid. Generally, taxes paid on foreign income entitles you to a deduction or a credit. The credit is usually the better option. You can see more about that here.