to get rid of mill glaze and open the pores of the wood to accept the sealer.
Depending on what you use to clean it, you may need to brighten it.
They do make cleaner/brightners in one.
Clean and brighten it just as you would any other deck. You want to open the pores on the wood and remove any mill glaze that may be present on the surface. The oxalic will ultimately do this. Do a splash test after the deck is dry to insure its porous enough to absorb a finish.