There are many ways you can do this and the best option depends on your game design.
You must tell us first what is your PSI game all about. Is it platformer, top down shooter or what, then we can respond more appropriately.
I will give you a simple example for flying shooter case:
- create a global variable called "weapon" as numbers.
- in event sheet, in your key press event (for example "press Spacebar") , have the following events:
- - if global variable is 1, create instance of object Bullet at player's sprite
- - if global variable is 2, create instance of object Laser at player's sprite.
- - if global variable is 3, create instance of object Bomb at player's sprite.
The above is simple event to handle a ship having multiple weapons but only one can be used at a time.
Should you want to use a different weapon, you might perhaps use an event like this:
- if keyboard key 1 is pressed, set global variable "weapon" to 1.
- if keyboard key 2 is pressed, set global variable "weapon" to 2.
- if keyboard key 3 is pressed, set global variable "weapon" to 3.
Now with this, the player can select weapon with a key press of 1,2, or 3, and fire respective weapon with spacebar.
If you understand all above, proceed. Else please say so that you still need assistance and we could assist you further.
Now, if you understand all above, you probably have a general idea with simple weapon switching mechanic in event sheet right now. This could be done similarly with skills in your game.
To do the remaining thing, such as "unlockable skill", "player using skill in specified button", "mapping skill to specified button", "power levels in skills", etc. ,these could be a little challenging if you never play around with programming before.
On the basic level, if you understand why do we have variables, and how to use them in the events, you could simply use number variables for simple indexing to refer to each skill like I did above.
But before I say anything else, tell me first, what is your game genre and what are your character's behaviors for each skill. Because if we dont have more info, we will not be able to assist you in finer details. As of now, I can only provide you with a rather very general idea of weapon/skill implementation above, which might not be able to answer to what you really wanted.
Also add my name "@keroberos" in your next reply so I can see if you need further assistance.