Portrait Collage Instructions
Portrait Collage Instructions (easier method/shorter video, Photoshop)
Portrait Collage Instructions 2 (harder method/longer video but you will learn some more things about Photoshop)
Google Drawings (this works if you don't have access to Photoshop)
Adobe Spark (even easier because it gives you a template, but I want you to know how to do it in Photoshop so you have full control of the creative process from start to finish)