On the app, click start or the "+" button > Click "Album" or "Motif" to select pictures and/or videos > Click the check or next button > Add music under "Find music" or "my music" > Click next to edit your clips.
When you're in the edit screen, you can now select each clip (circle thumbnail) for more clip-level options (Filters, stickers, add title, etc.). When you’re done editing, click the download button at the top right and select “Create Lomotif”.