Welcome to the forum
@wonderoona !
It is easier to use their cell phone. The second tab on the phone is travel. Click on the Sim you want to travel (the panel photos of your Sims at the bottom of the screen). To add Sims with whom you want the first Sim to travel, click on travel with, and then, click on their faces in the pop-up menu, which comes up automatically.
Cancel all of the actions in their queue before you travel. After that happens, the screen will get white (but you can still see where your Sims are). You will see a small purple car in their queue, and it will say travel.
Then, you'll be brought to the map, and you can choose to which lot you want them to travel. If you want them to travel to a different world, click on the world icon in the upper left corner of your screen on the map.
P.S. I just started TS3, so I just had similar questions about TS3
. They're both very different, but both TS3 and TS4 have great qualities!