When Story progression is on, you will get Sims in you're world. Same goes for players who have installed you're world. If you want you're own Sims, you can do this:
- Install you're world, make you're families as you normally would do and place them in you're world.
- Save you're game, exit the game en look for you're game here:
C:\My documents\Electronic Arts\The Sims 3\Saves.
- Selected you're saved game, right click --> copy to compressed zip folder.
- If you have a program like WinRar (nagware), 7 zip (freeware) of FreeArc (freeware) you can also use that to right click --> add to archive (see
here). Download links for those programs see
here (it's a Dutch site but it speaks for itself). After you add to archive you get a zip file.
- Upload the zip file to a site like Mediafire of Box.
- The link you are provided with you can include in the description of you're world or in you're topic (in you have one) you have opened about you're world, or in you're blog, or ... whatever. Upload first you're file before you upload you're world so you can include this link in the description.
- Players can now download you're families and you're world. Only, after they have unpacked this file, players have to put it with their Saves folder in My documents.
I think (have red) it's best to make and place families before you start to play you're world.
EDIT:
Or you offer you're families by exporting them from the game. So players can download them separately. If you use the Exchange, players can download and install them through the launcher.