Secular humanism is the belief that humans do not need a god. That we can be good, ethical and successful without one; and even though we did not realize it, we have often been doing that for a long time.
Christians sometimes have a more inclusive idea about secular humanism. They would include the above, but also any activity or organization that does not include god, such as football and public eduction.
At death? A secular humanist, who is an atheist, would simply believe that at death we die, no second life. So you better make the best of this one because it is the only one you get.
We do not suffer because of Satan or evil or the first sin, we suffer for the same reason all animals suffer; the world is a hard place to live. It seems to be difficult to get the resources each person needs to every person. This planet has, for now, enough for everyone but some of us hoard resources (the rich) while others have none. Also evolution did not evolve humans on purpose and we are subject to all the problems and complications that other animals are, such as competition for resources, disease, and lack of knowledge.