Putting the cahin back on???duh???

Not always the same from year to year. Just Google "install chain coaster brake bike". It's easiest if you have a tool to size the chain. If you have a bike co-op or community bike workspace in town they can help.

If a one speed coaster brake the rear hub needs to be overhauled. Take to a bike shop or bike co-op, unless you want to look up, study and follow carefully: Bicycle Coaster Brakes

I’m happy to help further over the phone at https://www.6ya.com/expert/donald_f2ed37026a3ac881

I 'm not an exprt on bikes but the chain depends on the gears. If gears are same, you can use the same chains. So, all you should check if chain fits gears.

remove the coaster brake lever bolt. This is small bolt that holds the coaster brake lever to the left side chain stay. There will probably be a strap wrapped around the chain stay with bolt going through the strap and the lever. This usually requires a 10mm wrench (sometimes it is 8mm) for the nut and a Phillips or flat head screw driver (some times it's another 10mm bolt head).
The axle nuts are usually 15mm nuts. Loosen these (they usually don't need to be removed all the way) and push the wheel forward to put some slack in the chain. Lift the chain off the rear cog and you will be able to pull the wheel out of the drop outs.
To install, slide the wheel into the dropouts, put the chain back on the cog, pull back on the wheel and tighten the nuts finger tight. Reinstall the bolt through the coaster brake lever and then tighten the axle nuts, pull back on the wheel while tightening the nuts so the chain is tight. Then tighten up the coaster brake lever bolt. (if you tighten the axle nuts first, you won't be able to move the coaster brake lever into place to get the bolt in)

Only if it has a freewheel, it will make a slight clicking sound when pedaled backwards. The coaster brake models do not. If you pedal backwards and the cranks locks up tight after moving a few inches then it is a coaster brake bike. These also have a brake arm on the rear hub, attached to the frame.

Buy a standard chain taht is compatible with your cassette (number of gears in back) and size it according to this advice...

http://www.parktool.com/blog/repair-help/chain-length-sizing

You should be able to go to a bike shop and they would be able to cut a length to size for your bike if not I have had luck lawn mower shops they do carry chains

are you trying to replace the sprockets? you can't get the nut off because it spins? just put the bike in gear and remove the front gear first, leave the chain on until after the nut is loose. also "make sure you flatten out the nut lock first".

I'm guessing this bike has a rear coaster brake. I really don't suggest overhauling a coaster brake hub and it is unlikely a diagram for your huffy exist but here is a link to a general coaster brake hub diagram. It should be very similar to what you are working on.

http://www.wtlw.net/ff/suntour/

Hope this helps!

you can tighten the coaster brake by turning the big lever on the back tire