The reliability of wikipedia depends on what you are using it for and the nature of the information. I would not rely on wikipedia for knowledge regarding something highly contested, or in an academic context. However, you're not really going to find people with an axe to grind about Latin grammar. So without having seen it I'd suppose that it is reliable.
More to the point, I recommend using one of the many freely available textbooks to learn Latin. Rather than reading grammar summaries, you should be learning it in a structured and pedagogic environment. There are many textbooks available to download on this website (D'Ooge, for example), and many modern ones to be purchased cheaply via Amazon.com or elsewhere.
Horae quidem cedunt et dies et menses et anni, nec praeteritum tempus umquam revertitur nec quid sequatur sciri potest. Quod cuique temporis ad vivendum datur, eo debet esse contentus. --Cicero, De Senectute