string.PadLeft() / PadRight()

// Returns a string padded on the left with spaces (or a specified character) to reach totalWidth.
str.PadLeft(int totalWidth)
str.PadLeft(int totalWidth, char paddingChar)

// Returns a string padded on the right with spaces (or a specified character) to reach totalWidth.
str.PadRight(int totalWidth)
str.PadRight(int totalWidth, char paddingChar)

// Returns a string with format placeholders replaced by the given arguments.
string.Format(string format, object arg0, ...)

using System;

// Use PadLeft() to right-align numbers (align digits in a column).
for (int i = 1; i <= 5; i++)
{
    string line = i.ToString().PadLeft(3);
    Console.WriteLine(line);
}

// Use PadLeft() to zero-pad a number.
string code = "42".PadLeft(6, '0');
Console.WriteLine(code); // 000042

// Use PadRight() to left-align text.
string[] items = { "apple", "banana", "cherry" };
int[] prices = { 150, 80, 300 };
for (int i = 0; i < items.Length; i++)
{
    Console.WriteLine(items[i].PadRight(8) + prices[i] + " yen");
}

// Use string.Format() to build a formatted string.
string message = string.Format("{0}'s score is {1} points.", "Tanaka", 95);
Console.WriteLine(message); // Tanaka's score is 95 points.

// You can also format numbers (e.g., two decimal places for a percentage).
double discountRate = 0.1567;
Console.WriteLine(string.Format("Discount rate: {0:P1}", discountRate)); // Discount rate: 15.7%

In modern C#, string interpolation ($"{variable}") is often preferred over string.Format(). Format specifiers such as :P1 and :D6 can also be used with string interpolation in the form $"{value:format}".

To zero-pad a number with PadLeft(), you can also use a numeric format string such as number.ToString("D6").

For splitting and joining strings, see Split() / string.Join().