If you have V3 when your an adult, click on it you will fly to a destination and get a code. However if you have V4 wait untill the "Travel Agency" opens in the V4 Tama Town because if you dont wait then you wont get your souvenir!
(1) wait until your Tamagotchi is an adult. If it's not an adult, you can't use the ticket.
(2) use the ticket. Have a paper and pencil ready for the password. Select the ticket in your item list and use it. When the password appears on your Tamagotchi's screen, write it down.
(3) get a souvenir password. Go onto TamaTown, and enter the travel shop. Click on the computer in the travel shop, and when prompted to do so, enter the password from step 2 above.
(4) claim your souvenir. Go into the password section on your Tamagotchi, and enter the souvenir password from step 3 above. A travel souvenir will now appear in your souvenir list on your Tamagotchi.