Simple e-learning template

You may also find this video tutorial helpful. https://youtu.be/BZhASnzcNCQ

It's not exactly what you asked but close enough that you should be able to get the foundation of what's needed. By the way, there are over 250 other videos that are available on my channel. https://youtube.com/paulwilsonlearning 

If you are very new, go to YouTube, search for Paul Wilson Captivate and subscribe to his channel.  You will learn a couple of good things like the Advanced Actions mentioned by Lilybiri. Happy learning.

Very new? Your scenario is not so simple as you think. You will need shared or advanced actions and variables to solve this. First requirement is to understand Captivate's Timeline, how you can pause that timeline and define conditions. It is essential to tell which version of Captivate you are using (full version number please). If you are on CP2017 (10.0.0.192) the Advanced Actions dialog box has been refurbished. I will not post screenshots since I'm not sure what you use. Can you read this post:

Challenges for Starters - Captivate blog

You will see that template has a speical meaning in Captivate, it is a cptl file. I strogly advice never to use such a template since there are several issues. But I suspect you are not really talking about a cptl file, but about maybe a master slide (which is part of a theme).

You created 3 buttons, are those shape buttons (more flexible than the legacy buttons)? You seem not to be on CP2017 where (shape) buttons have 4 InBuilt states: Normal, Rollover, Down and Visited. That would mean that you added one extra custom state which I will label 'Active'? On former versions the 'Visited' state would be custom as well.

Because of the requirement for the appearance of the Next button, and the fact that there is no imposed sequence to click the buttons, you will have to define 3 user variables for tracking: v_one, v_two, v_three. They will be Booleans, give them a default value of 0 which will be toggled to 1 if the associated button has been clicked. I suspect that you also allow multiple clicks on each button?

Actions in Captivate are event-driven: you have the Success event for each of the buttons to trigger actions, and those actions have to do everything: changing the variable, showing the text and the picture (which can have the audio attached to it, will save you one command), changing the state of the button, checking the variables to show eventually the Next button, and changing the state of the two other buttons. There are several approaches possible: either you have indeed those different items on the slide, but hidden in output, or you use a multistate object with custom 3 states: normal state is an empty shape (no alpha, no stroke), the other states correspond with what you want to show.

From the length of my answer, you should have understood that the complexity of your question is bigger than you suspected. Would it not be better that I suggest a much simpler approach to start with, to allow you to get to grips with variables and advanced actions?