This article is from the Atheism FAQ, by mathew email@example.com with numerous contributions by others.
Many atheists live a purposeful life. They decide what they think
gives meaning to life, and they pursue those goals. They try to make
their lives count, not by wishing for eternal life, but by having an
influence on other people who will live on. For example, an atheist
may dedicate his life to political reform, in the hope of leaving his
mark on history.
It is a natural human tendency to look for "meaning" or "purpose" in
random events. However, it is by no means obvious that "life" is the
sort of thing that has a "meaning".
To put it another way, not everything which looks like a question is
actually a sensible thing to ask. Some atheists believe that asking
"What is the meaning of life?" is as silly as asking "What is the
meaning of a cup of coffee?". They believe that life has no purpose or
meaning, it just is.
Also, if some sort of mystical external force is required to give
one's existence a "meaning", surely that makes any hypothetical god's