Unity will scale things the best it can to adapt to different screen resolutions - however it will always maintain the aspect ratio of the original artwork.
An image you drag into the hierarchy is considered a sprite. This is a non-UI element. Typically this is a character or background element.
The image set through UI is considered a User Interface element. This is used to make panels that display information - like an options menu. UI image sprites also support some great functionality like 9-slices (you can scale an object without distorting corners) and masking. You can also do quite a few tricks with the UI to have it adapt to different screen resolutions.
I defiintely recommend checking out Unity’s training here if you haven’t already:
Thank you ! So sprites will outomatically adapt and ui elements (button ect) will have to be anchored sliced ect to stay the same? Thats pretty good since im more worried about gameplay than buttons looking thrle excact same.
So do I just have to trust that unity will show Sprites the same across all devices (and how good is it at doing that)?and I will read more of that link so thanks!