Console.ReadLine() / Console.ReadKey()

// Reads a line of text input (confirmed with the Enter key).
string line = Console.ReadLine();

// Waits for a single key press and reads it.
ConsoleKeyInfo key = Console.ReadKey();
ConsoleKeyInfo key = Console.ReadKey(bool intercept); // Pass true to suppress display on screen

using System;

// Read a string with ReadLine().
Console.Write("Enter your name: ");
string name = Console.ReadLine();
Console.WriteLine($"Hello, {name}!");

// To use the input as a number, you need to convert it.
Console.Write("Enter your age: ");
string input = Console.ReadLine();
if (int.TryParse(input, out int age)) {
	Console.WriteLine($"Next year you will be {age + 1}.");
} else {
	Console.WriteLine("Please enter a number.");
}

// Use ReadKey() to wait for any key press.
Console.WriteLine("Press any key...");
ConsoleKeyInfo keyInfo = Console.ReadKey();
Console.WriteLine(); // ReadKey does not add a newline, so we add one manually.
Console.WriteLine($"Key pressed: {keyInfo.Key}");
Console.WriteLine($"Character: {keyInfo.KeyChar}");

// Branch logic based on a specific key.
Console.WriteLine("Select Y/N: ");
ConsoleKeyInfo choice = Console.ReadKey(true); // Does not display the pressed character on screen.
if (choice.Key == ConsoleKey.Y) {
	Console.WriteLine("You selected Yes.");
} else {
	Console.WriteLine("You selected No.");
}

Because Console.ReadLine() returns a string, you need to convert it using int.Parse() or int.TryParse() if you want to use it as a number. Always validate user input.

Console.ReadKey() is well suited for UIs that respond immediately to a single key press, such as pausing a program ("Press any key to continue") or navigating a menu. Passing true to intercept suppresses the echoed character, making it useful for implementing password input.

For writing output to the console, see Console.WriteLine() / Console.Write().