If you understand evolution as you say you do then give me the one answer I have been looking for here. Give me an example in the fossil record of how a fish became a dog or any kind changing into another kind. I want just ONE fossil that proves this. But there isn't one. There is no concrete evidence otherwise. These so called "transitional fossils" are not enough evidence to support this. The fossils that are found are one that show micro-evolution, which is basically adaptations that happen within a species but not outside of the species. Changes do and can occur within a species for sure but dogs cannot mate with cats, and so on. Also, mutations are not observed as beneficial in our world. They lead to major problems, such as Down's syndrome and other serious issues. The only "solution" is to throw unobservable millions of years at the problem and then that is called good "science." That is pure speculation without any evidence to support it. The evidence supports that animals cannot mate outside of their own kinds and when changes do happen because of mutations problems occur.
Have you seen the study done by researchers at Michigan State University where they reproducibly saw the evolution of one type of bacteria into another type of bacteria when they carefully constrained the food sources available to the microbes?
To understand evolution, keep in mind it is generally a divergent process, so species A becomes species B and C, not a convergent one where species A and B join to make species C (except on the microscopic level, like how amoeba-like organisms joined with blue-green algae to form plants). An easily understood example is the split between the Chimpanzee and the Bonobo: they were one species until less than a million years ago, but then two populations were separated by the Congo river, with the bonobos on the south and the chimpanzees on the north. Neither can swim such a large river, and so the populations could not intermingle. The two areas have different climate and food options, and so the two populations diverged into two species.
OK, since you are about the same understanding level as a 6 year old, this is how I explain evolutionary paths to my daughter in 1st grade: If you go back in the fossil record, you will find a time when there were fish but no dogs (or any other land animals). There were many types of fish, some ray-finned fish like a goldfish, and some lobe-finned fish like the lungfish. Lobe-fins look like legs, in fact some of these creatures moved onto land and adapted to breathing air and walking and they became salamanders. Some of the salamanders stayed salamanders, but some of them developed scales and eggs with shells, which allowed them to live away from the water, those we call reptiles. Some of these reptiles stayed reptiles, some developed hair so they could stay warm and milk to feed their babies, these became mammals. The first mammals might have looked something like large shrews. Some of these survived by eating meat of other animals and developed into the carnivore class, like wolfs. At some point some wolves and people started living together and the people selectively chose the animals which were good companions and we now have the modern dog.
A somewhat related note, I was once watching a documentary about dogs, they mentioned that the dog family has a stretch of genes where the physical characteristics are stored (size, shape, color), but unlike most animals the dogs have this section copied a whole bunch of times, causing a huge amount of variability. So many changes can be made to the dog physical appearance and bred to what is desired. This is why breeding dogs has led to such a huge variance in dog appearance in a single species, while other animals like cats or horses have a much smaller range of breed-able variance.