To begin, you'll need to download a collage-making app from the App Store - there are tons to choose from, but some popular ones include Canva, Pic Collage, and Adobe Spark. Once you've got your app, open it up and start browsing through the different templates and designs - you'll find everything from simple grids to whimsical shapes and patterns.
Now it's time to start adding your photos to the collage - this is the fun part! Just tap the + icon to add a new photo, and then resize and rearrange it to your heart's content. You can also add text and stickers to give your collage a little extra personality.