And what is meant by evolution?
A change in the number of inheritable traits over time. E.g., if the number of short-haired individuals in a population of bears goes from 5 to 5000 over 100 years, then that population has evolved.
Natural selection is the mechanism by which the 'short hair' trait becomes more frequent, though you'll notice that there is room for God to have a fiddle.
Does it mean we all started out as a single celled organism and evolved to humans. Or the monkey to human.
Basically. The original, common ancestor of all life bred and bred and bred, and its many offspring evolved, eventually leading to several species, which each in turn split into new species, and so on.
One species splits into two, separate species. Originally, the group can all interbreed. Later, the group has split in two, with one side not being able to breed with the other, and vice versa. Once that happens, any new genetic information that crops up (e.g., a gene for short hair) cannot cross over into the other group.
So, each group becomes more and more genetically distinct, and split into several more species.
Is evolution also just evolving as a specie as opposed to evolving into another specie?
It's both, yes.
Is it possible we have always been human and things have changed over time. Did we have large jaws like the neandrathal and once we discovered fire and started cooking meat our jaws got smaller. What about wisdom teeth. Are there evolutionary processes at work here too. Some people never even get those teeth. I don't mean to be obsessed with jaws and teeth but it was the only example I could think of. lol
That's fine, teeth are a good example of human evolution. Our ancestors had large jaws and a large skull, but our particular lineage evolved to become bipedal: we stood up. The only way for this to happen was for the skull to get smaller - while this lead to detriments like a cramped mouth, the benefits were worth it.
(I think; I'm not a biologist, I may have got the details wrong!)