Solidity is similar to Javascript, but also has similarities with C++. If you are new to object oriented programming languages like C++, and are unfamiliar with any terms that you encounter, then you can refer to this glossary or to an educational website for C++ such as learncpp.com. Alternatively you can learn Python first (e.g. with docs.python.org or Learn Python the Hard Way, which I found to be rather condescending), then Javascript (e.g. with MDN), then C++, since Python is the easiest to learn, and C++ is the hardest of these three.

The following glossary list is ordered roughly from the simplest to the most complex. Topics at the top of the list tend to be a precursor to understanding topics later in the list.

  1. Logical operators
  2. Relational operators
  3. Assert
  4. Keccak. Note that Solidity doesn't use the newest specification available, it uses the one submitted to the SHA3 competition.
  5. Ripe MD