How can I get the pictures on the windows10 tile app into 'my pictures

Please can someone help me. I have purchased an Internet offer for a collage which requires me to upload my pictures which I have selected and have in a folder in the Windows 10 picture app on my PC. However, when I go to the sellers site to proceed with the sale I press the upload picture button and I am taken to 'my pictures' on my computer which does not have the folder in it. Please can anyone help me as there was no other option for uploading other than from 'my pictures'. I am not at all technical and the offer has time constraints....any help would be greatly appreciated.

If you open the Photos App and then click on one of the pictures you want to upload you can then right click on the picture and select open folder. This will take you to the folder where it is stored. Hopefully you will see where it is and can find it later for your upload.