To create a message in the E-Business suite message library you will need the “Application Developer” responsibility.
Navigate to Application Developer > Application > Messages. This will launch a form

Enter a unique name for your message
Eg: XX_CUSTOMER_MSG
Select the language that your message is written in and the application that the message belongs
Enter the message text in the “Current Message Text” box.
Eg: This is my first message
Click the save icon.

Retrieving a message using PL/SQL:

In order to retrieve the message from the database we need to use a standard API’s in the FND_MESSAGE package.
An E-Business suite message should be retrieved as follows:
1. Clear the current session of any message variables that may already be set
2. Tell E-Business suite which message you wish to retrieve
3. Retrieve the actual message string
4. Clear the session (Optional)

Below is the PL/SQL Block to retrive the message

DECLARE
 my_message VARCHAR2(100);

 BEGIN

  –Initialize Apps Session
  fnd_global.apps_initialize( user_id      => 1234
                             ,resp_id      => 1235
                             ,resp_appl_id => 1236
                           );
                         
  /*–Note: You will get the uer_id, resp_id and Resp_appl_id using below Query
    select fnd.user_id ,
         fresp.responsibility_id,
         fresp.application_id
  from   fnd_user fnd,
         fnd_responsibility_tl fresp
  where  fnd.user_name = ‘OEAG’
  and    fresp.responsibility_name = ‘Custom HRMS Responsibility‘;
  */
 
  –Clear the existing session
  FND_MESSAGE.CLEAR;

  –Tell e business suite which message you want (custom application short name/message name) 
  FND_MESSAGE.SET_NAME(‘XXERP’,’XX_CUSTOMER_MSG’);

  –Retrieve the message
  my_message := FND_MESSAGE.GET;  

  –Output the message
  DBMS_OUTPUT.PUT_LINE(my_message);
 END;

Output for the Above Block Is : This is my first message

Using Tokens in the message:

The Oracle E-Business suite allows the substitution of tokens within a message string to enable the programmer to add dynamic content to the message at run time.
Open the E-Business Suite message create a New Message
Navigate to Application Developer > Application > Messages. This will launch a form

Enter a unique name for your message
Eg: XX_UNAME_TOKEN_MSG
Select the language that your message is written in and the application that the message belongs
Enter the message text in the “Current Message Text” box.
Eg: This is my second message and the Token User name is &USERNAME
Click the save icon.
Note: In order to insert a token into a message it is necessary to prefix the token with a ampersand e.g. &USERNAME
Retrieving message With Token Substitution
Here USERNAME is called as TOKEN, we will Add the value dynamically

Example Block  is below:

DECLARE
 my_message VARCHAR2(100);
BEGIN
 –Initialize Apps Session
 fnd_global.apps_initialize( user_id      => 1234
                            ,resp_id      => 1235
                            ,resp_appl_id => 1236
                           );
                         
  /*–Note: You will get the uer_id, resp_id and Resp_appl_id using below Query
    select fnd.user_id ,
         fresp.responsibility_id,
         fresp.application_id
  from   fnd_user fnd,
         fnd_responsibility_tl fresp
  where  fnd.user_name = ‘OEAG’
  and    fresp.responsibility_name = ‘Custom HRMS Responsibility’;
  */
 
 –Clear the existing session
 FND_MESSAGE.CLEAR;

 –Tell e business suite which message you want (Application short name/message name)
 FND_MESSAGE.SET_NAME(‘XXERP‘,’XX_UNAME_TOKEN_MSG’);

  –Set the username message token with the current applications user
 FND_MESSAGE.SET_TOKEN(‘USERNAME’,FND_GLOBAL.USER_NAME);

 –Retrieve the message
 my_message := FND_MESSAGE.GET;

 –Output the message
 DBMS_OUTPUT.PUT_LINE(my_message);
END;

Out put for above block is : 

Downloading and Uploading Messages using the Generic Loader

To download our example message we would use the following command at the Unix prompt on the mid-tier:
 
FNDLOAD apps/apps 0 Y DOWNLOAD $FND_TOP/patch/115/import/afmdmsg.lct XX_UNAME_TOKEN_MSG.ldt
FND_NEW_MESSAGES APPLICATION_SHORT_NAME=’PER’ MESSAGE_NAME=”XX_UNAME_TOKEN_MSG”

To Upload our example message we would use the following command at the Unix prompt on the mid-tier:

FNDLOAD apps/apps 0 Y UPLOAD $FND_TOP/patch/115/import/afmdmsg.lct XX_UNAME_TOKEN_MSG.ldt