What is the Meaning of .Replace("*", "%")

You can get the answer yourself by writing few lines of code. Isn't it the beauty of programming that you get the result immmediatly?

Anyways, try this:

string input = "***Lets try to understand Replace function.*** Should not be that diffcult ?";

           Console.WriteLine(input);

           Console.WriteLine(input.Replace("*", "%"));

           Console.WriteLine(input.Replace("?", "_%"));

I hope you get the answer yourself. Trust me, it gives a great feeling. :)
Read more about it here:

http://www.dotnetperls.com/replace[^]

http://msdn.microsoft.com/en-us/library/fk49wtc1.aspx[^]

Textbox1.text.trim().Replace("*", "%") . it replace all "*" with "%" in textbox1.text

if in textbox1.text has
"What is * profit in my * investment"
it will become
"What is % profit in my % investment"

It returns a new string; in which all occurrences of a specified string in the current instance are replaced with another specified string.

In your example Textbox1.text.trim().Replace("*", "%") it just replaces all '*' with '%'
Refer: String.Replace Method (String, String)[^]

Also have look on: C# Replace[^]

Replace function replace with Old character with New character

Eg :- if Input :- str= Microsoft

str = str.Replace("o","B");

Then output is: MicrBsBft