So basically you do need to declare it, but it depends a bit on where your clients are from. If they're from the US, they're gonna want a W-9 or a TIN (tax identification number) from you so they can pay you properly. Now, if they're from other countries, things get a little looser, but you still need to declare your earnings to the IRS anyway.
What you do is keep all the documentation you have - bank statements, emails with the agreed amount, invoices if you issue them, basically any proof that you received that money. With the IRS you're gonna declare it as self-employment income, and you'll probably need to fill out a Schedule C (if you're in the US) or the equivalent, depending on how you're set up. The truth is the IRS wants to see everything that comes in, so the more organized documentation you have, the better it is for you.
One thing a lot of people don't do but should is set aside money already to pay taxes, because if you're getting a lot of freelance income, by the end of the year you could owe a considerable amount. Some people create a structured business to make it clearer, but being honest, if it's just been a few months still, you can try to sort everything out when you file. I recommend talking to an accountant who understands international freelancers, because they know exactly how to make this less complicated and not leave room for problems later.