How do I create array in actions?

Can you post the events that aren’t working? People will be more willing and able to help if they have a starting point. Otherwise, it’s just a lot of guessing.

What type of an array? A simple array or an array of structures?

Make sure to set the variable as an array in the appropriate setup screen for global, scene or object.

You can then use one of the array actions to add the value or variable. If you want to set a specific index then you can use

variableName[#] The # can be a number, variable or any expression that returns a number.

https://wiki.gdevelop.io/gdevelop5/all-features/variables/#accessing-child-variables-in-structures-or-arrays

This might also help.