"Greeter" is a very simple app made with Textual. All it does is to "greet" the user in the output field. Enter your name in the "input field" and then push the "Submit" button.

app.py

from textual.app import App, ComposeResult
from textual.containers import Horizontal
from textual.widgets import Footer, Header, Static, Button, TextArea


class MyApp(App):
        
    def on_mount(self):
        self.title = "Greeter"  # This line set the app's title
        
    def compose(self) -> ComposeResult:        
        yield Header()
        yield Static("Please enter your name:") # Adds a label
        with Horizontal():
            yield TextArea(id="input", text="Will McGugan") # Add a text field for the name
            yield Button("Submit", id="submit_name") # Adds a button to submit the name
        yield Static("The app response:") # Adds a second label
        yield TextArea(id="output", text="...") # Adds a text field for the output
    
    def on_button_pressed(self, event: Button.Pressed) -> None:
        if event.button.id == "submit_name":
            name = self.query_one('#input')
            output = self.query_one("#output")
            output.text = f"Hello {name.text} !"


if __name__ == '__main__':
    app = MyApp()
    app.run()