I have given you a starting point and mentioned 2 possible approaches to solving this problem. Investigate them and try one, I'll gladly help you towards a solution but I'm not going to write the solution for you.
Try to solve the problem using string manipulation check
this MSDN entry, it contains explanations on ALL the functions which you will need. Try to create a solution using these functions, if you get stuck post the code, explain where you got stuck and I will help you further.
Start by creating an algorithm which will find the tags within a body of text, once we have that aspect we can look at extracting the text between tags.