Welcome Mindi/ I upload photos here to post all the time. In fact I have no photos stored on my laptop so they only come from my phone.
Try this:
1) At the bottom of the post, click on the option "Upload an image".
2) My phone shows the most recent photos I have taken. Or I can click on the "hamburger", the three lines at the top left for more choices of where my photos are stored, like the 'Gallery' on my Android.
3) Choose a folder or photo. click "Open" at the top of the page.
4) Dave has already programmed in a photo link for your and it will show up as "lightbox".
5) At the bottom of the page it allows you to "add another photo" , click on that if you want to share more photos and follow the same order above.
Hope this helps!