The first tip I’d like to cover about this spankin’-new application is how you’ll go about adding your images to existing albums. First, if you just want to do this with Photos in the same way you did with iPhoto, you’ll have to turn the sidebar back on (View> Show Sidebar).
Then you can drag and drop your images into albums there as you’ve always done.
Here’s one of the new ways that you can accomplish this same task, though, and I think it’s much easier. Whenever you’re viewing the Photos, Albums, or Projects tabs at the top of the program’s window…
…there’s a plus button that’ll appear on Photos’ toolbar. If you click it with nothing selected, it offers to make you a new item (such as an album) of your choice.
If instead you select some photos first and then click the plus button, you’ll see that the text “Add [number of] Photo[s] To” has appeared at the top of the menu.
Click on “Album,” and within the subsequent window, choose either to create a new album with the selected images or add them to any existing albums or events.
I find this to be so, so much simpler than the old drag-and-drop method, especially for folks who have dozens of albums. Of course, Photos (like 10.10.3) is still in beta, so it’s possible this feature will change before the program’s final version is released, but I sure hope not. Apple, I like this. I like it a LOT.