Here's a specific example of how monthly blankets benefit you as a new player: When you start with 15 Build and buy one Monthly Blanket for 30 Goblin Stamps, you'll gain one event day's worth of Build, which brings you to 20 Build total. Buying a second Monthly Blanket for 30 more Goblin Stamps brings you to 25 Build total. A third Monthly Blanket brings you to 29 Build (since the amount of build you get per event day diminishes over time), a fourth brings you to 33 Build, etc. After you attend your first weekend event at 33 Build, attending the weekend event itself brings you up to 39 Build, for example.
Note, however, that you can only buy Monthly Blankets for the current month and 3 months prior to the current month (which means you could get Monthly Blanket credits for December 2014, January 2015, February 2015, and March 2015 at the moment, but not any months further back from that or in advance).
If you're interested in getting a few blankets for your first event (starting out with more than 15 Build is always nice), you could check out SoMN's donation list and see if there's anything you can bring to get you some Goblin Stamps to spend on blankets. I look forward to seeing you come out to our events this year!
~ Alexander