Intro

Blockchain - decentralized technology, a global network of computers, continuously growing list of records, called blocks, which are linked and secured using cryptography. Value-exchange protocol where exchange of value can be completed more quickly, more safely and more cheaply than with traditional systems.
Cryptocurrency - digital asset designed to work as a medium of exchange that uses cryptography to secure its transactions, to control the creation of additional units, and to verify the transfer of assets. They use decentralized control as opposed to centralized electronic money and central banking systems. Each cryptocurrency works through a blockchain, which is a public transaction database.

https://coinmarketcap.com/

Market Cap - size of a total market or individual cryptocurrency. Price x Circulating Supply
BTC Dominance - % of money invested in Bitcoin. If it rise, altcoins will probably loose value (bleed)
Volume - important factor where we can see what's on trade and what's on hold.
Circulating Supply - the best approximation of the number of coins that are circulating in the market and in the general public's hands. Coins that are locked, reserved, or not able to be sold are coins that can't affect the price

What is the best cryptocurrency?
Very difficult question to answer since teachnology is very young. When choosing a crypto to buy consider the following:
Does the coin/project have a purpose and solve a problem? The team behind the development? Does it have long-term potential and a roadmap? You can click on each crypto in coinmarketcap and you'll find links to website, announcements, source code etc.

Crypto terms: