When you post a question on Brainly, at the bottom left side you can see three symbols. One of symbols is that of a clip or what you call a paperclip.
When you double click that icon of a paperclip, a box will appear which will ask you to choose from the options: 'take photo or video', 'photo library' or 'iCloud'.
Choose the option from where you want to upload the picture from or choose 'photo library' if you want to upload a picture from your gallery.
