There are many IT professionals that are involved in the creation of enterprise software (which is basically software that is created by business to solve a particular challenge of clients/customers). When it's all said and done, two types of IT professionals are responsible for writing the code that wills the application to life and maintaining said code; they are the frontend software engineers and the backend software engineers.
The frontend software engineers/developers are responsible for all the anesthetics on software solutions, anything you see (pretty or not) is as a result of the frontend developers (devs for short). The backend software engineers are the ones who build the logic of the software, they're the ones that enable the software solution to accept some data from you and give you some information in response to your actions or requests, they're the reason why you can enter your details into an app and be allowed to log into the service.
Frontend code and backend code are usually in different programming languages, it might make some wonder how these languages are able to work in synergy, there's a popular programming language called JSON (Javascript Object Notation) which acts as the middleman and helps mediate affairs between the frontend and the backend, transferring data back and forth. While it isn't the only one, it is however the most popular mediator.