Hi Aritz.
In your event sheet all you need do is create the condition for which you want to create the character (eg. on start of layout) then select 'Create Object' under 'System'. Then just choose the character and select the location :)
The best way to handle this however is to probably create a 'spawn' object and copy this across layouts and make an event that spawns that character at that object, then include that event sheet in each layout so you don't have to worry about it each time. Hope that's helpful!