First of all, you should probably talk to your boss about upgrading to the latest version of EE. 2.2.0 is quite old.
Secondly, you might want to start by reading the ExpressionEngine documentation, such as The Big Picture.
ExpressionEngine uses "channels" to store data, which are basically types of content (each with their own data structure). So in your case, you would probably create a channel called "testimonials", and give it fields such as "Author" and "Body".
You can then use the {exp:channel:entries}
tag to pull out random testimonials in your templates. I'm going to assume you are familiar with HTML and CSS, (otherwise you are going to have a very hard time using EE).
In your templates, you would use something like this (once you have set up the channels and added some data):
{exp:channel:entries channel="testimonials" order="random" limit="1"}
<h3>{testimonial_author}</h3>
<p>{testimonial_body}</p>
{/exp:channel:entries}
EDIT: After re-reading your question, it sounds like you actually want users to submit their own testimonials. In that case, everything above still applies, but you need to use the built in SafeCracker extension to allow users to submit channel entries on the front end. An overview of how to use SafeCracker is beyond the scope of this answer, so I'll leave it to you to read the documentation and feel free to post ask a new question here if you run into any specific issues.
I'll suggest though, make sure you understand the concepts of channels and entries before you bother trying to figure out SafeCracker. Work on creating the channel and entering testimonials in the control panel, then display these on your site using the tags above. Once you have got that far, you will have a much better understanding of how to use SafeCracker.