Uninterested is the opposite of interested. It simply means you have no interest in something:
He's totally uninterested in traveling. He likes where he lives and never wants to leave.
We approached the other company and proposed a partnership, but they were uninterested.
In casual spoken English, we tend to say "not interested" for the word uninterested.
The word disinterested means somebody is neutral. They have no bias (opinions that could unfairly influence their judgment). If two people are having an argument, they should present the case to a disinterested third party who can give a clear and fair evaluation of the situation.
However, some people do mistakenly use "disinterested" where "uninterested" would be more accurate.
Always be sceptical and wary. If someone asks to be friends on a social networking site and the profile appears to match a work mate, check personally with that person before accepting him as he could be an imposter. Also be sceptical of any offers or prizes you might have been told you won, they might actually be phishing attacks.