Milling is EXPENSIVE and yes, the slabs have to dry out before you can use them.

Then you have to run them through the planer to make them smooth, etc.

It's romantic as hell, but not very practical. I'd make firewood of it.

You might see if you can get someone with a portable sawmill to slice the tree up for a share of the wood.

It ten need to be stacked ad dried.
The typical air drying 'formula' is about one year for each inch of thickness of the cut boards.

Kiln drying small loads is a non-starter unless you want to build a kiln (not all that hard with thick insulating foam).

For most folk firewood is much easier.

Maybe save a few pieces to dry inside and use for small projects.

If the tree is urban(city) you will probably not find a sawmill willing to process the wood. Because people put metal objects in urban trees with amazing frequency---which destroy a several hundred dollar saw blade on contact.

You might find a portable sawyer with a mill, but those folks are also aware of the danger.

Transporting a pair of logs---16-20 feet is pretty much the limit for other than logging equipment---requires a front loader or large tractor with forks---and a trailer with boomers(chain tie downs) and chains---not inexpensive.

You could air dry the cut wood---after treating the ends with chemicals to deter splitting---and having a place with overhead protection---and stickering(separated stacking) the individual pieces so they can be rotated about every 6 months. Air drying takes about a year an inch---a 2" thick board needs 2 years.

Then---you toss the boards that warped---no real way to save those---and deal with the ones left---requiring processing equipment like jointers and planers.

What it boils do0wn to is no matter what you wound up building with the wood, that item would be very expensive---and could have been done much more inexpensively by just buying the already processed stock.