How do I get started in Second Life?
First, you need to make an account! Sign up here. You'll be prompted to select a payment plan (choose free), then brought to the download page.
Don't download the SL viewer! Instead, go to firestormviewer.org and download Firestorm! It generally runs better and has an easier to use UI for newbies. There are other alternative viewers out there, but Firestorm is the most widely used for daily use.
Complete the tutorial, and navigate to the SL Marketplace, or just click this link. You'll want to grab this, it includes many links to free avatars, some bento (animated) ears, and a dance HUD!
Once you've chosen an avatar, search for a sandbox and click and drag the boxed avatar from your inventory onto the ground (not all the freebies are boxed, most are. Some are ADD to unpack). Then, right click and select 'open', then 'copy to inventory'!
Find the unpacked folder in your inventory, and use common sense as to what to equip. Remember, always 'ADD' items, never 'WEAR' them! Usually, there will be a SHAPE and an ALPHA, you'll always want to equip those.
Congrats! You've just set up your first avatar!
As mentioned in the video, if you aren't satisfied with your freebie avatar, you can either make your own textures or purchase a modkit.