There are a number of ways to put your photos in order and export them. 
This is the method that I have found to be the easiest.  

Step 1:   Open your photos app on your Mac.

Step 2:  Go to the menu in the upper left corner and click FILE, NEW ALBUM.  You can name                    your album appropriately (ie, growing up, sports, family, etc.)

Step 3:  Repeat creating a new album for each section of photos.  If you are opting to have                the photos chronologically from start to finish then you will only need to create one                album.

Step 4:  Go to your photo library and locate the photos you would like to use.  Drag each                      photo into the appropriate album that you created in step 2. 

Step 5:  Within each album drag and drop the photos into the order that you would like

              them to appear.

Step 6:  When you are finished placing the photos in the correct order, go to FILE,                                    EXPORT, EXPORT ALBUM.  This will bring up a menu with options on how to export.                        Under  the "File Naming" section MAKE SURE TO CHOOSE:  Album name with number.                  This will keep your photos in the order you put them.  The photo to the right is the                    setting that you should use to export.

Step 7:  Once you have the correct settings click EXPORT.  That will bring up a window                           allowing you to choose where on your computer you  would like to save them.

Step 8:  Notify me that you are ready to upload your photos and I will provide a link for you                  to upload them.