Hi @marie9423498,
I highly recommend you check out this recent webinar on the lead score: https://www.youtube.com/watch?v=KvT3cY09pWQ
It explains a lot of the rational and there are recommendations on how to use each score type.
In the end, both types of scores behave very similarly to the old score, resulting in a custom property, not an object. What has changed is the user interface to configure these properties.
If you want to combine two separately created scores, you can easily do so with a simple sum formula in the custom calculation property builder: Create calculation and rollup properties (calculation property = score1 + score 2)
Best regards!