typically slabs are cut thick, then dried and planed/resawn to the final desired thickness. This helps to reduce checking, splitting and warping.
When drying green lumber, you want to promote air movement. so don't bury it in sawdust or stick it under a tarp. Slabs should be stacked with small boards (called stickers) to promote air movement. You can let slabs sit in standard air and dry out, it takes about 1 year per inch of thickness to achieve "dry".
You can also build a kiln of sorts that uses solar energy to speed the drying process.
There are some good resources on YouTube on milling your own lumber. I have a list on my school computer that I show my students. I will try to remember tomorrow to post some links.