Ok the fish are holding at 25 feet. How do I fish a slab or jig at a depth of say 25 ft. Then they move to 15 ft. How do you know how deep your lure is, and how do you keep it at that depth while retrieving it at a speed that will attract the fast movers? I'm new to "out in the lake" fishing. I'm not land locked any more! Any advice is appreciated.

Also I have seen some markers anchored in fishing spots. Is it ok to tie up to someone's floating spot marker and fish?

You can count pulls. Normally from the reel to as far as your arm will reach or the first guide is 2'. A slab should pretty much fish straight down.

^^^ What he said works best for me. Drop your lure to the water surface and hold the line with one hand while pulling from the reel to the first guide which is about 2 ft. Continue counting down to the depth the fish are holding.
Or cast out and count it down to when it stops falling. That will tell you how many counts it takes to get to the bottom and divide that number to get an approximate depth before reeling in. It isn't as effective as vertical jigging usually though.

Also, I wouldn't tie to any buoy or marker. They belong to someone else. It is illegal to tie to any buoys that mark hazards or wake zones, etc.
Those little orange or green markers people use to mark their spot are not weighted enough to hold anything stationary.
The larger floats are probably someone's trotline, so that's not advisable either.
Just use your anchor or get an I-pilot and spot-lock would be the best.

I use an Ambassadeur 5500 LC. When spooled to the full spool level, it gives a very accurate depth indication of the lure. Watch the depth finder, and put it on their nose. It is a bit pricey at $110, but it is worth it for me. As new marks appear at a different depth, match the counter to the graph and start slabbing.

Moe's Tackle has a good instructional video for fishing slab spoons. Basically, just drop the slab to the bottom, jig it up and down a few times and reel it back up through the fish. The suspended fish will hit it on the way down or when you are reeling it back up. The speed depends upon the season. We have been having luck with a fast retrieve lately.

One of the easiest ways to know, is to measure how much line is reeled in with ONE complete turn of the handle. Have someone assist you in pulling out exactly 10 feet of line. Give the handle one turn and then measure to see how much line was reduced. This will give you a quick way of knowing what each turn will do to your depth. Now each turn won't be exactly the same as the circumference of the spool is slightly different with line let out or taken in, but it will give you a very accurate estimation.

If you are fishing 25 feet deep and want to raise to 15 feet and each complete turn raises it 24 inches/2 feet (example) then 5 turns of the handle would raise the lure 10 feet you are right where you want to be.

Thanks for the input. I watched the video.

I do this or peel off line to the first guide. You can drop your lure to the bottom where you know the depth and count the handle turns to the surface to get the feet per turn of the handle.