There are various ways to do this, but I'll be teaching you one of them I managed to find out myself. In case of getting one idea on your own, feel free to suggest it and I may add it (I'm new to this forum so I don't know if I'm actually able to edit my own topics) to the main post so others can look at it and try it themselves.
With that said let's start our tutorial here.
Button Press Hint
As the name suggests, we're going to make a hint appear after pressing a certain key. This gimmick requires no script, but may be very tedious at the time of using it. You'll see what I mean after reading the entire tutorial.
Step 1: First of all, we need to create an event, but not any kind of event, the trigger must be set to Parallel Process. Why? Because we want the event to activate any time throughout the game on which we are able to move. Autorun would not work as we want it to be in this case due to not allowing the player to move the character, since Autorun events are in the very meaning of the word, endless.
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Step 2: Next, we have to set a Switch Condition. Why? The Parallel Process event will run always as long as we're on the map that is located, with the exception the player will be able to move, so that's ok. But if there's another event currently running and press the button that will trigger this event sometimes the hint may appear when it is not supposed to. The Switch is set with the purpose of not allowing the hint text to appear. At the beginning of each non-hint event there has to be a command that will set the Switch to OFF, disallowing the event to run when the same key is pressed, and at the end of the same non-hint events there has to be a command that will set the Switch to ON.
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NOTE: Before continuing be sure to check RPG Maker VX Ace default controls. Keeping them in mind be sure to pick the best button for the hint to appear. You can check them running your game and pressing F1.
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Step 3: Now that we have set the event conditions and we have choose a button we can move on to the event commands. Right click the commands window and click Insert to add a command. Click the Conditional Branch right below the Flow Control section and a new window will pop up. Go to the fourth page, select the Button condition and the button you want as the trigger (In my case, I'm using L, which on Keyboard is defined as Q).
IMPORTANT NOTE: Do not forget to uncheck the "Set Handling When Conditions Not Apply". If you don't, as you might guess whatever you set to happen when this condition applies will endlessly run.
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Step 4: After clicking ok, we should have the following event.
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Now, next, above Else we set the text that we want to make appear as the hint, whatever we want. And below Else we leave it as it is, as whatever we put below is what will happen if the condition does not apply, and we don't want anything to happen if the condition does not apply, otherwise the player wouldn't be able to move depending on whatever we insert there.
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Congratulations! You've just succesfully made a Hint event. Now whenever you press Q (Or whatever key you have set as the condition) this text will appear.
But what is this? There's only one hint, and the hint will only appear on the map we have created. But don't worry, we can fix that. First, if we want more hints after, I don't know, completing a quest, what we have to do is create a new Event Page that will run only if a event that activates a Switch is ON. In other words, if we want another hint to replace the one we have, we just need to add a Switch Operation command that will turn ON a certain Switch, which at the same time will trigger another event page of the same hint event with the very same commands, but the hint shall be different.
This solves the problem of adding more hints, but what if we want the hint to appear somewhere else? That's easy to fix. The hint will only appear whenever the event is located; in other words, if we want the hint to appear somewhere else, what we have to do is copy the same event with all hints to all maps where the player would be able to get hints of what to do next.
Hope this turorial has helped you, thanks for reading.