You'll find the brief on the campaign's page.
Go to "Campaigns" at creators.thecirqle.com/creators/collaborations.
Open the campaign.
Click the "Campaign Brief" tab.
When a brand selects you, you'll also get an email titled "You've Been Selected for a Campaign with [brand]" with a link straight to the brief. Each task has its own instructions too, which you'll see when you open the task.