Get a good gardening book. Forums will only take you so far.
If you want to improve the soil, read about composting, double digging and other methods to improve soil quality. Dumping fertilizer will do nothing. Building good quality soil takes time and effort and will take a few years before you've really made a difference. I suggest starting with small beds and a small plot for vegetables, get some really good organic compost delievered, get those beds in decent shape and slowly work on improving the lawn in general. This can be done by tilling the sandy areas, working organic matter into the soil. Also, stop raking your leaves and throwing them away. Compost them. Or, leave them on the lawn and in the spring, till them into the top layer and overseed with some quick growing grass. Do this again in the fall and again in the spring.
The last thing you should do is buy bags of "turfbuilder" or other such stuff. Good healthy soil takes a lot more than just dumping bags of chemicals on sand. You have to slowly build up a healthy layer of humus and that only can occur with the addition of organic material.
Many homes are left with no topsoil after being built. It takes quite some time to rebuild it.