(This card is always treated as a "Blue-Eyes" card.) This card is treated as a Normal Monster while in the hand or Graveyard. When this card is Normal or Special Summoned: You can target 1 Spell/Trap Card your opponent controls; banish it. During either player's turn, if your opponent controls a monster: You can Tribute this card; Special Summon 1 "Blue-Eyes White Dragon" from your hand.
Since it's treated as a normal monster when in your hand or grave, you can use normal monster support cards to special summon Dragon Spirit of White multiple times. This lets you banish a spell/trap card your opponent controls whenever it's summoned too. You can also Dragon's Rebirth to special summon Dragon monsters from your hand or grave. If you're using a Dragon only deck, then it's more useful to use, but the monster used as the cost is banished, instead of going to the grave.
Since it's always treated as a Blue-Eyes card, you can use Blue-Eyes support cards. Majesty with Eyes of Blue is a good way to send a Blue-Eyes to the grave from your deck. This can help with special summoning it later with cards like Birthright, or Beacon of White. Beacon of White for a potential OTK in certain decks. If you use Dragon Spirit of White in a BEWD deck, you can also bring Burst Stream of Destruction for an easy monster removal.
Blue Dragon Summoner can't be used to get Dragon Spirit of White from your deck since it's not a normal monster when in the deck. But Blue Dragon Summoner can get a Blue-Eyes White Dragon.
A combo that you can do is that if you control Dragon Spirit of White, you can normal summon Blue Dragon Summoner and use Enemy Controller to take control of your opponent's monster to get a BEWD, then you can activate Dragon Spirit of White's effect to special summon BEWD from your hand. This can only be done if your opponent still controls a monster, so it's mostly only beneficial if your opponent has 2 or 3 monsters for a potential turn around.
Paladin of Felgrand can equip Dragon Spirit of White if it's in your deck. This sets you up for a special summon using Birthright later. Alternatively, if you already have Dragon Spirit of White in your grave, you can equip Arkbrave Dragon instead. When Arkbrave gets sent to the grave, you can special summon Spirit of White to banish a spell/trap card your opponent controls. If it's too slow, you can use Paladin's effect to special summon Spirit of White right away if you have another monster on the field.