[CalvinC]

Start off by showing the dialog in OnPlayerConnect:
https://sampwiki.blast.hk/wiki/ShowPlayerDialog
It should be a DIALOG_STYLE_LIST ofc.
Then you can check what the player picks using listitem in OnDialogResponse:
https://sampwiki.blast.hk/wiki/OnDialogResponse

Read those 2 wiki articles, there's also examples.