Is this site absolutely free?
I am just wondering if this lessons are free. How often do I need to sing in to be able to learn Spanish quickly?
Yes everything on this site is free. The lessons, flashcards, forum... all of it is free.
Yes, you do need to sign in in order to do a lesson (as you do to post in the forum). The site tracks your progress (lessons completed, scores, etc.) so the system needs to know who is doing the lesson.
It is absolutely free. You're progress will be determined by your past experience and your determination.
Never stop learning for more than one or two days at a time, even if it is just a little bit a day, try not to stagnate for too long. You'll see measurable progress in a month, but progress is different for each person.