I will back Jorgen on this one, do NOT use EF as your data access layer if you intend to become a serious developer who builds data centric solutions. Linq to SQL is basically a disaster wrapped in obscure syntax, learn TSQL and you will reap the benefits your entire career.
Never underestimate the power of human stupidity
It seems, that the express-edition does not have all the tools installed.
There are different installation options for SQL Express - the larger "Express with advanced services" or "Express with tools" downloads include Management Studio, whereas the smaller "Express" download doesn't.
You'll need to pick a starting date, since different months have a different number of days.
For example, 30 days from 1st March would be 30 days; from 1st April, it would be one month; from 1st February 2014, it would be one month and two days; from 1st February 2012, it would be one month and one day.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
Just noting that if your intent is that your application will be doing all of the database administration then choosing a database that is less full featured might be a better option. And choosing an embedded database might be a better option as well.