Adding Salt to My Pool

[DOMSPOOL]

My pool is a salt pool, its been sitting for a year. Ive shocked it and gotten most of the leaves out.
My question is when do I add the salt to the pool and how long before you can swim?
My pool store says I need 18 bags of salt to get it back up to par.
and where do i add the salt, just throw it in the pool or skimmer?
thank you Dom