To be able to charge people, you need a system capable of charging credit cards. I strongly recommend you look at Stripe. Their system integrates with virtually anything. There are no monthly fees - they take a small percentage every time you charge a client or customer.
You also need a checkout system. This is the system where clients are entering their billing details, including card numbers, so you can charge their card using Stripe. I strongly recommend Thrivecart. They currently charge a one-off fee rather than a monthly fee, and it's a bargain for all the functionality you'll get. Trust me - offering your products and services with Thrivecart will make your life easier!
Then there's the mailing system - being able to automate all of your emails when someone wants more information from you, or when they purchase a product or service, is critical to your success. ActiveCampaign makes this much easier. If you do not already have a mailing list system, click on the link and buy ActiveCampaign.