How do I create a Email template in ASP.NET

That is a facility that a form provides. Not an Email template!

What you need to do is to create a simple form that has some basic fields like I am a student/teacher, I would like to choose [course] from your [institute]. These are the only things that will differ in each of the email. So you can design the HTML for that. Suppose the following,

<form method="post">
   <!-- Basic fields -->
   <!-- Name of the application -->
   Name <input type="text" name="name" />
   <!--  His type, student or a teacher-->
   I am a <select name="type">
             <option value="student">Student</option>
             <option value="teacher">Teacher</option>
          </select>
   <!-- Course code -->
   Course code <select name="course">
                  <option value="845">845</option>
                  <option value="846">846</option>
                  <option value="847">847</option>
               </select>
   <!-- Application that he will fill out -->
   Application <textarea name="application"></textarea>
   <!-- Input button -->
   <input type="submit" value="Submit" />
</form>

..this is enough. Now since you said that you're using ASP.NET (in the tags) I would use the C# code to provide the remaining template of the code that you will write to enable this feature.

// variable initialization
var name = Request["name"];
var type = Request["type"];
var course = Request["course"];
var application = Request["application"];

// checking if the request was POST
if(IsPost) {
   // working out the EMAIL
   // you can add your own validations such as 
   // if name is not null or empty string
   if(name != "" && name != null) {
      WebMail.Send(to: "recipient_email@example.com",
                   subject: "Application recieved", 
                   // create the body of the email.
                   body: "Thanks for applying " + name + 
                         "\nYou applied as a " + type + 
                         " for the course code " + course +
                         " and your application was as \n" + application
                  );
   }
}

Once this is sent, it will contain the dynamic data from the user. You will need to design your HTML as to enable the user to select from some provided tools and options. Then use those values and populate the HTML email.

You can learn more on sending emails using ASP.NET, from this article. Sending Emails Easily Using ASP.NET Helpers[^]