Proxies

I don't know anything about this topic, but I have heard of proxies.

What I want to learn:
What are proxies?
Why are they useful or not?

Links:
http://www.optimum7.com/internet-marketing/technology/what-are-proxies.html
http://www.techterms.com/definition/proxyserver
http://proxy-services-review.toptenreviews.com/what-you-need-to-know-about-proxy-services.html

What I learned:

• Protect your information.
• Allows you to view websites and their information without them receiving your information.
• They work  for security purposes but they can also be used to block access to websites.
• There are several types of proxies: Catching Proxy Server, Web Proxy, Anonymizing Proxy Server and Hostile Proxy.
• Catching Proxy Server- Speeds up user's request.
• Web Proxy- Filters content.
• Anonymizing Proxy Server- Anonymous web surfing 
• Hostile Proxy- Captures information about webpages and forms users fill/visits.
• You can't really know if the proxy server is really protecting your information or just collecting it until your identity is compromised.

Summary:
     Proxies can help me protect my information while I'm web surfing, but there's really no way to know if it really is working or not. There are several types of proxies with different purposes. If in a future, I choose to open a company I can also use proxy servers to block access to my employees to some websites. Also when I'm older and have my kids, I can use proxy servers to control what sites they go to and block contents.

Questions:
Is there a way to get around proxies? (hack them)