User experience is to enable your customers to use and feel whatever you are offering to them through your web page/app/software.
User Interface(UI) & User Experience(UX) are the initial yet most crucial touchpoints of the customer lifecycle. Both UI and UX are IT terms and interconnected.
User experience is to enable your customer to use and feel whatever you (the business) are offering to them in a delightful manner. While the User interface is to design and develop the website, app or other technical gateway is a way where the client can experience your offerings in a smooth way.
Let us put it in this way, suppose you are a manufacturer of commercial UAV/drone. For a better UI/UX point of view, you need to develop a simulator that can work on your website/app so the client can virtually experience the flying experience and understand the control manual. This way you can simply beat the competitor and one step closer to get your client onboard.