Where do I being to file a corporate tax return?

Investments aren't taxable. You need to make sure you have proper documentation from your investors showing either their membership interest (LLC), shares (C or S Corp), or other article of organization showing their ownership interest in some way.

You are required to pay taxes on revenues earned, but in many cases you aren't required to pay unless you cross a certain threshold. Each state has its own laws, and you can search "Department of Revenue for [STATE]" in Google and find the best way to record your revenue and taxes.

Once you get enough revenue, hire a firm like ADP to do your payroll processing and also set up the corporate tax payments through them. This makes things easier, but does cost money.

Since you didn't mention how your entity is set up or where you are doing business, it is hard to give specifics.

I would strongly advise engaging a good CPA for this type of work. There are implications and complexities. I would not advise that you try to do this on your own. I know there are business owners who do their own taxes, but my own experience has taught me that a good CPA is worth his or her weight in gold for the headaches (and savings).