For anyone interested in the single player challenges:
To summarize, there are five different scenarios that present you with different starting situations and restrictions. You'll be competing with others for the fastest time, with some time penalties that will be applied for ignoring parts of the challenge. These scenarios will harder than a typical Manager skirmish, some significantly so. Don't be discouraged if you have trouble with some of them (A Warm Welcome and Best Served Cold, in particular).
Detailed instructions for how to access the scenarios is in the google doc, under the Instructions tab. For submitting times, either join the Discord server linked in the first post and PM DeathTacticus or Blues, or add one of us on Steam and send the messages there (http://steamcommunity.com/id/BluesOTC). Be sure to note the specific screenshot requirements for each scenario, which are listed in the google doc and in the scenario description. You may submit times as often as you'd like, without penalty, and only your best time will be kept.
Good luck and have fun!
EDIT: Just a quick note that if you want the in-game descriptions of the challenges, you'll probably have to have the game set to English.