Salt nicotine is refined differently from traditionaly refined nicotine It is designed to give an instant hit but be a smoother vape than traditional nicotine at the same strength. So a 10mg will feel like a 3mg on the throat and a 20mg will feel like a 6mg on the throat but with the head feel and strength of a higher nicotine. This helps satisfy those that need higher nicotine but find traditional nicotine harsh.
Salts come in 10ml bottles flavoured and usually in strengths of 5mg, 10mg & 20mg. There are also salt nicotine shots for adding to short fills these however are duluted in 0mg liquid to create larger bottles than the 10ml that salts are usually found in.