To collect payments from your customers, you need to first have the Payment Gateway integrated in your Shopify Store. To select what Payment Gateways are available in your country, check the following link : https://www.shopify.com/payment-gateways
Once you select a Payment Gateway, connect with them manually and they will be connecting the payment gateway with your current bank account. As soon as the process is completed, you need to ask them to provide Credentials for Shopify Integration and they will provide you.
As soon as you get the credentials, follow the below process :
Go to Settings (bottom left on your Shopify Admin Panel) > Payment Providers > now connect your payment provider using that credentials.
There are multiple ways to collect your payments from customers. In Alternative payment methods you can also set Cash On Delivery option for customer
And if you find any query in general, please connect with me on email@example.com
Nick here from Shopify.
As @Lemolite highlighted you would first need to add some payment gateways to your store. If you are in any of the countries below you can add Shopify Payments if you wish, if you are in a country other than the below, there is a list of the Payment Gateways partnered for each country in the link here.
The steps you would need to add a payment gateway to your store can be found below:
Store Admin > Settings > Payment Providers > Here you will see a page similar to the screenshot below where you can add the gateway of your choice according to the country you are based in:
All the best, Nick