Soil is the combination of the mineral (sand, silt, and clay) particles and organic matter that we grow things in. Topsoil is the top 4 to 8 inches of soil, that may or may not include some organic matter. The volatile part of the soil equation is the organic matter, compost, vegetative waste.
In your soil you want to have about 6 to 8 percent organic matter, and that will need to be replaced annually.
In addition to a good reliable soil test for soil pH and major nutrients perhaps these simple soil tests will be of some use.
1) Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drainsâ too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

Here is a link that might be useful: what is topsoil

You occasionally need to add more material because of settlement, its completely normal.

New beds will settle more at first. After they get established, go through a couple growing seasons, the settling will diminish.

Compost is organic matter, it will continue to decay and if you use mostly compost your beds will slowly sink.

Soil is mostly mineral matter, does not decay away but will have 'fluff' when you add it, which will also sink down and compact a bit over time.

So add a mixture of mostly topsoil and some compost, and you'll have plenty of organic matter. Once the level is where you want it, you can maintain soil organic matter with annual additions of compost.

Oh, and think about punctuation, your post is a little hard to read. :-]

Florida sand has zero tilth, and averages around one percent OM. That is why many gardeners in FL use the boxes filled with bought OM, like you are doing.

There are various problems:

One is that the OM is too high - plants need some mineral content in the growing medium.

Another is that most OM material is not fully balanced in plant nutrients, so some fertilizers are required.

Another is that raised beds easily dry out in strong florida sun, even in the summer. Digging the material down more level into the sand will help a lot with moisture retention, the plants will appreciate the mineral content of the sand, and then keep everything well mulched with leaves or hay.

Another is that after a few years of growing the same few crops in small areas the nematodes will infest. It's very important to rotate with legume crops quite often.

I have planted a bunch of Marigolds in my garden too cause I was told that the marigolds will stop and kill the nematodes too any other flower plants should or can I add into my garden like Nasturium,Zinnias,Sunflowers etc???What do Nematodes look like???
I did also notice flys once in awhile flying around my garden I make my own compost too but it is not ready to put it into my garden as of yet I know it needs to break down quite abit before I can put it into my soil also???

Some Nematodes are beneficial while others are harmful. Some Marigold do have properties that will control certain species of nematodes while many of the cultivars of Marigolds have had that bred out of them.
Most nematodes are microscopic, not visible to the human eye without strong aids.
There is a lot of information, as well as misinformation, available about plants the repel.

Here is a link that might be useful: About Nematodes

Anyone who has not gardened around the gulf coast is not likely to know anything about predatory nematodes, that's one thing. They are especially bad in florida sand.

The way to avoid them is to keep fertility high (best way to do that is with drenches, initial mineral and compost amendments and then continual high-quality mulch - like tall mixed grasses or if you are near the coast gather seaweed) and most of all do not grow the same crop in the same general spot more often than 3 or 4 cycles at a minimum.

I think the entomologists at the University of Florida know something about nematodes.

Here is a link that might be useful: About Nematodes

Yes, they obviously do since they garden in Florida. Some others don't know anything about them, however.

The OP should know this: there is no need to use poisons to avoid nematodes, just as there is none to use them against fungi, insects, or weeds.

I try to never have nasturtium or morning glory IN my garden! They can easily take over (as they did my herb garden!)
I have plenty nearby, though, and pick out any seedlings I find. Nancy

There are dozens and dozens of insects and diseases that can potentially harm your garden. The operative word is 'potentially'. There's really no point in fighting this one or that one that you happened to hear something about, unless you are observing some damage that indicates you have a problem with that particular pest.

There are probably a few nematodes in almost every garden, it's only when they get out of hand that you need to worry.

Of course I don't know Florida so maybe everyone has nematode problems there. If so, take this with a grain of salt.

Tox, nematodes are quite possibly the number one problem for gardeners in Florida. The warm climate and extremely low OM sand seems to be the reason.

The most common advice is to completely avoid the sand but I think that is a wrong-headed approach not to mention very expensive per sq ft.