OneDrive Mobile
1. Install OneDrive in App Store or Play Store

2. Sign into Microsoft Account

3. Select Plus icon at bottom-right

4. Select Upload

5. Select Photos and Videos

If it's a document from another app then you would share that document to OneDrive from that specific app, not on OneDrive.
If it's a document in your iPhone file directory, then you would use the Browse option.
6. Select Allow Full Access

7. Select photos you want to upload then select Add at top-right

8. Wait for Progress to complete

9. After completion, select My Files

10. Confirm your files are in the root directory of OneDrive

11. Access from your Desktop PC

You can save your photos/documents to a specific folder by going into My Files first then going into the folder you want to save your things into and then hitting the plus icon at the bottom-right. Hitting the plus icon at home will save your items in the root directory of OneDrive rather than a specific folder.