There are a few different ways to get your pics into PicMonkey, for editing.
Add via the Create New button (one image at a time)
Click the Create new button at the top of homepage.
Choose where your image is stored, from the dropdown list under the button. (Your computer, your Dropbox, OneDrive, Flicker, Instagram, Google Photos, or Google Drive folders)
Navigate to the photo you want and click it; it opens in the editor.
Upload to Hub from your computer (bulk upload method)
Click the monkey icon in the upper left corner to get to Hub.
Click the folder in Hub you'd like to add your photos to.
Click the upload button (cloud icon with an up arrow) that appears in the upper left corner of the gallery of images.
Navigate to where your images are stored, and select one or several of your choice, then click Open.
Once an image is stored in Hub, you can just click it to begin (or continue) editing it.
Add an image to an existing design
With your image open in the editor, click Add image button in top toolbar
Choose the place your photo is stored from the dropdown menu, navigate to it, and click Open.
Your photo shows in the left panel, under the "Uploaded" tab. Click it to add it to the existing image.
Upload to PicMonkey from a mobile device
Follow these steps to upload photos from your phone to PicMonkey's hub. Note: this does not involve using the PicMonkey mobile app.
Open the web browser on your smart device (iPhone, Galaxy, iPad, etc).
Go to PicMonkey.com on your device.
From the mobile homepage, select Go to my Hub.
Click the cloud + arrow icon.
Select the source to upload your pics.
Your uploaded pics are now accessible in Hub from a mobile browser, the PicMonkey mobile app, and on the desktop version of PicMonkey.
Upload photos via the PicMonkey mobile app
Open the PicMonkey mobile app (Get the app).
Tap the plus sign in the bottom toolbar.
Tap "Upload photos and videos.
Select the photos to upload.
Click "Upload to Hub" (they will be in your Unsorted folder unless you choose a specific folder before step 3 above).