All of my photos were in Picasa on my PC and on a flash drive. I am trying to transfer them to iPhoto on my MacBook Pro. What’s the best & most efficient way to do that? I am still learning how to use the Mac, so please be specific. Thanks!
Toss the pictures into one big folder and let iPhoto organize them for you. Using a thumb drive, copy all your pictures from your PC to the Pictures folder on your Mac. Open iPhoto and allow it to import all those picture into its database. If you do it one folder at time, you will be able to import them and arrange them at the same time.
Format thumb drive to fat, than use that to transfer, plus you will have a backp.
I think that the flash drive might face compatibility issues while connecting it to your Mac.
So,what you can do is to upload most of the images to dropbox,Google drive,Box and then use their respective apps so that they become available to your Mac and then import all of the images(i.e. copy paste) into a folder(s) and then it might get added into iPhoto.
I don't have much experience with either program but as far as I know Picasa uses a simple folder structure somewhere on your PC (probably in the "My Pictures" folder?).
If all your pictures are located in there all you have to do is copy that folder to the Mac and then drag&drop it onto the iPhoto icon. The default settings will automatically import and store them in the iPhoto Library.
* The original folder you "dropped" on the icon should be safe to be deleted afterwards but it's probably the perfect time to keep a backup of it e.g. on an external drive.
There is actually a Mac version of Picasa too if you are happy with that program.
Then all you'd have to do is use the export function of Picasa, store it on e.g. an external drive, then connect it to your Mac and run the "Picasa Restore.app"