How to obtain the player GUID depends a lot on the context of the event that drives the action. It can't be answered too confidently without more details about how you plan to have this work. If we dovetail with Branvex's suggestion, then it would be something like:

Code
IF
DialogEnded("DialogName", _ID)
AND
DialogGetInvolvedNPC(_ID, 1, _NPCGUID)
AND
DialogGetInvolvedPlayer(_ID, 1, _Player) 
THEN
CharacterSetFollowCharacter(_NPCGUID, _Player);


But again, this assumes certain things like there is only 1 player and 1 NPC involved in the dialog and that you want to assign the NPC to follow the player in the dialog regardless of any choices made in the conversation. Presumably you want to have some choice in the matter, in which case you would want to handle this with flags instead of merely ending the dialog.

I highly recommend spending time learning the language and going through some of the scripting tutorials out there. If you plan to create some kind of campaign, there is no getting around learning Osiris.

DOS2 Mods: Happily Emmie After and The Noisy Crypt

Steam Workshop
Nexus Mods