To be honest, the only things you really need to be able to do is read and type. The rest is mainly garnish. 
The main info hub is the Welcome Topic, and that’s got lots of links in for all the forum features (and you can dip in and out of that whenever you need to). There’s also a little Forum How-To that’s quite nifty. You can go to the Welcome Topic from any page by clicking on the ‘Learn More’ box in the main forum header banner.
For the reviewing and testing side of things it’s actually not as tricky as you’d think. It’s pretty much open to anyone. All you have to do is write some good reviews of things you’ve already got to get you started, and then pop your name down when a tester topic turns up. 
They can be quite popular, so patience is definitely a virtue, but new people get stuff all the time. 
With the main website getting a recent makeover the method has changed a bit from the The Great Big Review and Testing Guide, but it’s just as easy to chuck your hat in the ring.
If you go to the #testers category you’ll see the ones that are currently open for volunteers, and you simply have a read of the OP and reply to the topic with the items from the list you want to put your name down for. And if Brenna thinks you’re a good match she’ll pair you up with an item and send you an email.
The 
ones are regular testers that are already live on the site (so you can chat about them as you would any other purchase).
The 
ones are Secret, so those won’t have a product page as yet, and you mustn’t discuss them publicly anywhere (not even on the forum) until they go live on the site.
The The Great Big Review and Testing Guide is probably still worth a read even though it refers to some things that no longer exist (Tester List, Sex Toy Tester Wishlist, Linking Profiles, etc). The Secret Tester section is still spot on, and the sending in your measurements for lingerie testing (and the How to Write a Great Review guide is good too). I’m sure it will be updated soon with the new info, so keep an eye out for that.
Edit: And you might want to set #testers to ‘Watching First Post’ so you get a notification every time a new Tester topic is posted.
You can find out more on how to do that in Notifications