I'd skip the float for now, at least until next summer when you're more likely to be able to throw one against the winter gales ;-)
Simplest methods are... either a bubble float with a fixed lenght of trace attached to one end, around 6'.... you're looking at either short casts there or some kind of current to take it out. Not much use off a pier around here. Otherwise a sliding larger float weighted - stop knot is basically anything to stop it sliding up the line - a small narrow bore bead above the float and a loop in your main line with a small piece of thicker line between it will do (ie make a loop in the line to catch a stub of thicker line, like a half granny knot grabbing onto another piece). Length is anyone's guess, start at maybe 6' off a deep-water mark and increase a few feet at a time until you figure the area out..
Can't recall where you're from, but I think others have suggested going my way of fishing - simple gear, I've never caught a record fish (thought I had once and it made the Chronicle but it was a mis-identification.. See Alan Charltons post about "Shads" - "ohh bollocks was what I said!!!").. I catch loads of fish but mostly smaller common species and sometimes I hit on lucky for a while. Harbours, if you find a good one can produce, I remember S/Sluice harbour as a kid gave up no end of good sized plaice and flounder, last time I tried there it was dead. Wansbeck Estuary can have its good days. Rocks at Sluice I've had good fish but thrown so much gear away that I might aswell have gone to the chippy direct! lol.
Fishing is like anything else, if you don't get results at the start then it's easy to lose interest, that's why at 37yrs I've got a 20yr old electric guitar that I still can't play ;-) I listened to Ronnie Montrose and Eddie Van Halen and aspired high from the start!!! Take two rods to a harbour, one big rod and throw the bait out there for a long soak, take a little cheapy spinning rod and some small hooks/light weights and see what's hiding down the sides, I've had 2lb+ fish on the lightest gear down the edge - keep in mind where the food supply is, loads of shelter and therefore food for fishies down the edges in most harbours....
