Karlie here from the Shopify Support Team! If you have yet to make your first sale, then you can change your store's currency by following these instructions:
If you're looking for payment gateways to use, you can check out our payment gateway list, here. That list will show you what payment gateways are available for you to use from the country that you're selling from. You can use this guide to help you add the payment gateway of your choosing to your Shopify Admin.
I hope this has answered your question. If not, or if you have any further questions please let me know. I will be happy to help!