Hi Mary!
In order to get "credit" for that month's challenges, you must complete the challenges in the month that they are posted (ie you couldn't do a Feb challenge this month for credit). However, if life is busy and you miss a month... say you did Jan/Feb but then got busy and didn't get March done... you can skip March and then jump back in for April and still get credit for having done 3 months.
Basically, she just means that the months don't have to be completed consecutively.
I know it's a little confusing. Hope this helped a little!