@Xdresser10 there’s not much I can say to that, there are a lot more people that want to test than there are testers available so patience is key.
@TinaRosebud there is no specific timeline for being chosen, just be patient and keep popping your name down.
@Siamesecult you get an email from Brenna 
To become a tester, writing quality reviews for the items you already own (generally a minimum of 10 or so) is important, because that gives Brenna an idea of your writing style and what sort of items you would be suited to.
The Review Writing Routine, My Reviews and of course The Great Big Review and Testing Guide are all fabulous sources of information and examples of reviews