If you really want to know what it means to be a Christian, read the one of the Gospels (or 'Good News') in the New Testament section of the Bible. You may want to start with Mark - it's the shortest! The following link is to the first chapter in Mark's Gospel: Chapter 1
Why read the Bible? Because if there is even the tiniest possibility that the claims made in the Bible might be true, then it deserves our attention - If the Bible did turn out to be the word of God, wouldn't it be extremely unwise to have deliberately ignored it?
If you want to find out more about the claims of Christianity:
an excellent book to tell you why you should look into this further is 'Christianity Explored' by Rico Tice (ISBN 1-85078-383-7) available at Amazon. See the Preview introduction of 'Christianity Explored'.
There are a number of courses run by various churches:
the biggest is The Alpha Course which runs for 10 weeks and involves a meal, a weekly presentation (by the organiser or on video) and then an opportunity to discuss what you have heard. I choose to become a Christian after attending one of these courses.
Another course is called Christianity Explored; This has a similar format to the Alpha course, but is largely based on St Mark's Gospel.
A further option is the Y course.
None of these courses will put any participants under any pressure to do anything you don't want to do, so if you don't wish to speak, you don't have to!
I found the following definition:
It is an acrostic for the Latin words "Iesous Christos Theou Uios Soter," or "Jesus Christ the Son of God, Saviour." Before the meaning of this symbol became well known, the early Christians used it as a way to signal their faith to other Christians whom they did not know.
Although some have tried to detract from this symbol, and the Christian symbol of the cross as well, by pointing out that they had pagan origins, the important thing to early Christians was the significance that these symbols held for them, not what they held for others in the past.
Like their forefathers nearly two thousand years ago, modern Christians still use the fish symbol to signal their faith to one another, although the meaning of the symbol is by no means secret now.