if i put a screenshot photo in an album, and then delete the screenshot, will it still appear in my album?

Pictures aren't exactly "in" an album. When you put a picture into an album, its name is added to a list of pictures to display when the album is clicked, kind of like a music playlist, but for pictures. So two albums can both have the same picture name in their lists, and that picture will show up when you click either album, but there's only one picture file-- it's just on multiple lists. And when you remove a picture from an album, its name remains in the lists of other albums, and the file still remains in your Library of Pictures. 

The Library View shows a list of your entire Library of Pictures in the order they were "created." If you delete a picture from the Library View, then it is removed from the Library of Pictures, and it can no longer appear in any album list. The Recents View also shows a list of your entire Library of Pictures, but in the order they were "added." So, again, if you delete a picture from the Recents View, then it is removed from the Library of Pictures.

This is very cool, because you can have pictures in multiple albums without taking up any more space. The picture of "Aunt Ethel at the Grand Canyon" can be in the "Aunt Ethel" album with other pictures of Aunt Ethel, and it can also be in the "Grand Canyon"  album with pictures of other people at the Grand Canyon. Both albums are each pointing to a single file stored in the Photos Library. This is very powerful in organizing pictures, and it allows you to find the picture you want in several different ways.