A nuclear bomb has been detonated!

There aren't many if any threads about this on here, so I decided to start one.

I've been trying to learn about surving a nuclear explosion but I find alot of information contradicting or confusing.

So far I've realized that when you see the bright flash and you aren't dead, you have a chance to survive. Time to duck and cover like in the old cold war videos and wait for the blast wave to hit. Hopefully you are behind something that will shield you from the thermal and gamma radiation as well as the shockwave and debris that will pass you. I've read that if you are hiding and it hasn't hit you in 2 minutes then you are far enough away that it won't do significant damage. Not sure if this is true, but it sounds probable.

Now here comes the tricky part. After you have survived the initial blast how the hell do you survive the fallout? I remember Flight-ER-Doc (I think) posted something on this that shows different shelters. I've learned a few ideas too. Some involve digging a trench, other involving piling stuff on top of and around a table in your house. Either way it must be something to keep radiation back. The truth is, I don't know what would really work and what I would be able to come up with in a situation like that (I might not have the luxury of a premade shelter). I don't know what really would work to shield you from the radiation, protect you from breathing it, and how long some of these would take.

In addition to the concern of the shleter making itself are questions about fallout. Two important questions I've thought of:
1) How long can we expect it to be before fallout begins?
2) How long can we expect fallout to be dangerous?
I do realize that these questions rely on different variables.

3) Also, how big is the initial fireball on a nuclear bomb? This also is obviously something that depends on the bomb.

I raise these questions because if you do make a shelter, it will be important to know how long you have to be in there because without water and food you will be dead if it takes a long time. It also would be important to know how long you have to make a quick shelter.

It's certainly possible we will see a nuclear bomb go off in our lifetime, and I think we should have a discussion about what we would od if it happened.