Joanne,

There are several ways to download all the photos from your Google Photos to your hard drive, each has its pros and cons. Which one you choose will depend mostly on how many photos you have and whether you use Albums.

1. Download selected photos: select a group of photos (maximum 500 at a time) by clicking on the first one and shift click on the last, then click the 3-dot menu and choose Download. This will create a .zip file on your hard drive with all the selected photos.
   Pro: you are in control
   Con: lot of work 
2. Download albums, open the album, click the 3-dot menu and choose download all. this will create a .zip file with all the photos.  I use this technique because I don’t care about having ALL of my photos from Google Photos on my hard drive, but I do want the best ones. I have a system where I put my best pictures into albums by month, so, when the month is over I download that album to my computer – in an external hard drive. 
   Pro: nicely organized, just the best photos, easily found on my external hard drive because they’re labeled with Year/Mo
   Con: If you have years of photos, it will be a lot of work to download them album by album
3. Google Takeout: This is the system that Google Provides to easily download all your photos. Takeout.Google.com When you get there you’ll see that it is for ALL of your Google data, not just photos. Start by Deselecting all, then scroll down to Photos and select that. Next you’ll have the option to download all albums or just selected. These albums represent all your photos, not just the ones in your custom-created albums. If you choose to download all, it will divide them into .zip files of 2GB each.
   Pro: simple to download ALL of your photos
   Con: very hard to find any photos in the cryptic names of the .zip files
4. 6/12/19 note: this option will not be available after July 10, 2019 see Google article
   Google Drive, Backup and Sync: Google Drive can synchronize your Google Photos in the cloud with your computer.
      From Mrs. Geek’s Guide to Google Photos, Chapter 13: Google Drive p.121 (the ebook is available for members here)
       a. Using Google Drive (Drive.Google.com), turn on the setting to create a Google Photos folder in My Drive.
       b. In Backup and Sync, go into Preferences and click the Google Drive button from the left column. Check the box for Sync My Drive to this computer. Also check the box for Sync only these folders, then select the Google Photos folder.
   Pro: should give you a complete duplicate of your Google Photos library on your hard drive, no .zip files
   Con: Google Drive is complex, it can be difficult to see if it is really working right.

Sorry there isn’t a simpler answer. There really should be. But this is the state of things now.