The conditions of earth, a few billion years ago, allowed primitave amino acids and proteins to be formed. Eventually these built up the first simple, single-celled lifeforms. Cells tend to split as a mean of reproduction, so, after the cells advanced enough, there were probably some basic multi-celled lifeforms floating around. Now, as time progressed, lifeforms became more and more complex.
The question is: How could humans, composed of a trillion or so cells, with many complex immune systems and such, evolved from such a primitave lifeform? The answer: Natural Selection. Over billions of years of evolution, natural selection has weeded out the species with "bad" traits, and the species who were able to adapt continued to reproduce. Natural selection basically says that the species, in a given environment, with the most favorable traits will prosper the most in that environment. Similarly, a species with the least favorable traits will die out. An immune system just happens to be one of those "favorable traits" that allows us to protect ourselves from some harmful bacteria.
Now, time is a touchy area, since you cannot really imagine a "starting point" for time. Why? Well, if you tried to imagine a starting point, you are automatically bombarded with questions such as, "What was time a second before time began?" Because of this, time is probably either an actual dimension that had a beginning, and before this beginning there was nothing as we know today, or there is a negative timeline, branching off of the starting point as our positive timeline has. We'll assume the first hypothesis is correct for now.
As for the universe, I think that the physical dimensions as we see them, being length, width, depth, and time, were created as a result of our universe's creation. Since time is the 4th dimension, a concept that humans do not fully comprehend as of now, it is only logical to assume that for something to be created at "time 0" then time should have to be created at the same time. If we say that the universe was created at this "time 0," then it would also be logical to assume that time was created during this event as well. Because time was created as a result of the big bang, there was no time before hand, so, in a sense, there was nothing before the big bang that we can comprehend.
Furthermore, if we say that time was created during the big bang, then we can also assume that all laws of physics, and the other dimensions (length, width, and depth), were created at this time as well. Because the laws of physics did not exist prior to the big bang, anything really could have happened that we will never comprehend. That is, the laws of physics before the big bang might not be what they are now, and because of this we will never understand exactly how the first grouping of matter and energy were created. There could have been events that followed certain physical rules that do not exist today, or there could have been supernatural occurances in surplus because there were no laws of physics to bind them. I do not think we will ever know what happened before the big bang, since the big bang is the beginning of time for us.