Quantum mechanics is the description of the Universe, mainly on very small scales, as in subatomic particles. It has many weird aspects, that we are not accustomed to in our daily (large-scale) life.You can read an introduction to quantum mechanics, among other things, in the Wikipedia article "Introduction to quantum mechanics".

Books covering introduction levels to quantum mechanics can be found for sale on the amazon website or on the ebay bidding website. Alternatively the WHSmith store in the United Kingdom will have a similar book.

Richard M Sillitto has written:

'Non-relativistic quantum mechanics, an introduction' -- subject(s): Quantum theory

Principles of Quantum Mechanics was created in 1930.

The distinction is sometimes made to distinguish normal quantum mechanics (which does not incorporate special relativity) and quantum field theory (relativistic quantum mechanics).

Since we know special relativity is correct it is the relativistic form of quantum mechanics which is true, but non-relativistic quantum mechanics is still used, because it is a good approximation at low energies and it is much simpler.

Physics students typically study regular quantum mechanics before moving on to quantum field theory.