You will need to create relevant entities with attributes that fulfill your requirement of what data you need to take input for and store in database. Then you use the data view to create forms for it where you can take input from user.
On save button, call a microflow. There you can do things like call rest services, manipulate data, store data in database etc.
For REST call tutorial, see the documentation
If you are very new to Mendix, then you probably need to start with beginner learning paths so that you are able to create basic pages and take input as per your requirement