If you want to just learn notation and you're starting from scratch and know how to code, the linked article fits that description. However, notation for its o

If you want to just learn notation and you're starting from scratch and know how to code, the linked article fits that description. However, notation for its own sake is not really something I'd suggest sitting down and learning. If you have some maths you want to learn, the notation will come along with that, so any book or article that introduces the maths you want will also introduce the notation (usually building on some foundation level of existing knowledge, e.g. high school or whatever).