What the error means is that all the *create bits have to be at the top, with no *set or anything else until you’ve finished with *create.
Also, the “set” part of your code is unnecessary. Just have the hearts in the initial “create” part. For example:
*create health “”
*create strength “”
Better yet, make heart and strength both numerical values so they’ll be easier to manage in-game:
*create health 5
*create strength 5
Then if you want them to display as hearts in the stats page, you can do this:
*temp healthhearts ""
*if (health = 5)
*set healthhearts "♡♡♡♡♡"
*if (health = 4)
*set healthhearts "♡♡♡♡"
And so on. Does that make sense?