Click the camera icon on the right, then select images to upload. For each post, you can select up to 8 images. Tap the uploaded images 1-by-1 to rotate, delete, download images or apply filters for images.
As a reminder, once the images are uploaded, they'll be synced and stored privately and securely on the cloud. Then you may delete the already uploaded ones on your phone to save space as you need.
You can browse all your uploaded photos at the section "images".