There isn't a write-up on how to use Google Photos on mye28, so I figured I would write one to give people more options. I had to look up how to do it myself - it isn't the most intuitive process.
Start by logging in to photos.google.com.
Making a new album isn't necessary but I've found it helps with organization. Go to the break to skip album creation info.
Note: I don't believe you can upload from your computer and select already uploaded photos at the same time. If you're using already uploaded photos click "Done" next to "select from computer"
If you have a preexisting album you would like to add photos to, the "add photos" button is in the upper right once you select the album.
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Everything below here is the same, even if you don't use albums.
If you want to change the image size you can do that by modifying the giant url. The width and height are given in pixels all the way at the end. I don't think there are limits on what sizes you can use as long as you make it smaller.
Example:
Original size:
lh3.googleusercontent.com/lots_o_garbage=w2310-h1498-no
smaller:
lh3.googleusercontent.com/lots_o_garbage=w1280-h720-no