I want to use the long piece of wood as a tale top. The person that I got it from said that it Is not ready to do annoying yet. It still needs to be dried out. Do I just leave it in the sun and do it that way or is there a better method and for how long do I need to dry it out?

I would store it in your house for a long period of time and check it with a moisture meter periodically.

What are the exact dimensions of the slab of wood ,
the length , the width , and most importantly , the thickness ?

How long ago was the tree cut down and how long since the slab was milled from the log .
Do you have a photo of it ?

bump

It will warp unless you stand there and flip it every 20 minutes.
Put it up off the ground on blocks, in a dry working environment on leveled blocks and then put weights on it to keep it level, straight, or flat. Level or straight or flat ....is very important. Depending on the thickness, it may take 2 weeks per inch of thickness to "acclimate" to your working environment, in my experience.

If it's an old board/plank it won't take long. If it's just been milled off the log, then it may take up to 1 year to dry and acclimate.

Yup, need that info before and it would be helpful to know the species.

their are other good post's but i woundn't do this . Do I just leave it in the sun , that would be the wrong thing to do , the sun would start to warp it ,cup it and any other thing's that the plank desided to , good luck