Here is the official explanation of what the Activity is, which can be found on the same page where submissions should be uploaded:
LEGO House in Billund, aka Home of the Brick, is turning two this week, so let’s celebrate! We can’t think of a better way to celebrate than building your own, festive creations. Let’s see some brick-built cakes, flags, confetti, or whatever you find festive to honor the 2nd Anniversary of LEGO House.
This is part of a series on LEGO Ideas that gives little tasks for builders to get involved with – there are no prizes, they are just a way to get involved with building something quick for fun. Each challenge is intended to be something quick and fun, unlike the more in-depth building required for a competition or product idea.
The deadline for this Activity is September 30 at 10.00am CEST.
The last LEGO Activity asked fans to build a beloved pet.