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I'd suggest that you use diegoisawesome's tutorial. You're really better off reading than watching videos when it comes to scripting, especially because videos won't go over all of the options and syntax and they won't tell you why something is happening.
...Well, I'm generalizing, but it's better to get a basic grasp of scripting through reading and experimenting than starting out with videos.
You'll have to use scripting, and you'll be using a ton of flags. You can set flags which tells the game 'this thing has occured' and you can make the game check flags to activate different dialouge. Flags are very important in this process, so maybe looking into those should be a priority and getting familiar with checkflag and setflag.