@PJPineda : Here are my comments.
1. I'm assuming you mean that there was no conversation and that the person on the other end simply hung up after you answered.
2. You probably have nothing to worry about, other than the fact that the person/people/telemarketers at the other end now know that someone will pick up if they call your phone number. This may put your phone number on a "preferred list" for telemarketers.
3. I never answer calls from anyone that is not in my directory and all the people in my (home phone) directory have a "distinctive ring", so I can tell immediately if I need to answer.
4. If someone "important" calls that is not in your directory, they can they can leave a message.
5. If a name display comes up that you have dealings with, like a restaurant reservation, you can choose to answer or let it to to voicemail...
6. Sometimes a doctors office will have "private number" on the name display for confidential purposes. If you are currently dealing with a doctor, or similar, you can choose to answer if you want, or they can leave a message.