Hi Maria
Yes, Contact Form 7 lets people send you email without exposing your email address, and I use it for the contact forms on my site, along with the CAPTCHA plugin that goes with it......the CAPTCHA plugin isn't necessary but if you find that you're getting more than just the occasional spam from your contact form, you may want to consider adding that.
NO it does not subscribe people to your blog (RSS Feed or email).....to do that you either need to sign up for a free account with Feedburner, or use a paid service like Aweber, and get the form code from whichever service you choose, put it in a Text Widget, and drag the Text Widget into your sidebar.
With Contact Form 7, the default contact form works just the way it is when you add it to a page, but if you want to edit it, there should now be a button/link that says "Contact" below your Settings link.
You should have at least a basic understanding of HTML because the plugin doesn't add the HTML tags the way that the Post Write box does, but you'll see that it uses paragraph (<p>) tags to separate the fields, and you can modify the text that displays but DON'T modify what is in between the brackets (the [ and ] symbols that look like squared off parentheses).
You can either modify the default form, or create a NEW one, and I recommend creating a new one, then using the new one on your contact page - that way if you don't get it right you can always revert to using the default form.
There is some decent documentation that comes with the plugin and at their site on how to create new forms, but basically you just use the button in the upper right to generate tags that you can use in the box on the left to build your form.