Open Instagram and swipe right to open the Story camera
Tap the gallery icon
Select the first video
Tap the sticker icon
Add another video using the photo or gallery sticker if available
Repeat by adding more videos as stickers if supported on your device
Alternatively, create a single collage video in a video editor app first
Save the edited video to your phone
Upload the saved video to your Instagram Story
Use the multi-select option in the gallery if available to add several clips at once
Trim and arrange the clips before posting
Tap Your Story to publish