The biggest difference between slice and splice are whether or not they change the array. That means they have to be used differently.
You could certainly use either one in a solution, but you would use them differently because they are different functions.
If you show us the ways that you’ve tried to use slice and splice and describe what problem you having, we can help you troubleshoot. If you only ask why you can’t use them the same way we’re going to start by sharing documentation with you.