You may read the Ethereum Whitepaper here. Be advised it is technical in nature. The Whitepaper describes the various mechanisms of Ethereum and how its network is designed, as well as ways Ethereum can be used. There is also a technical doc on the ERC-20 Token standard here.

ERC-20 is a standard which allows Ethereum to be used to create something known as a Token. A token is often used in tandem with some exchange of utility which is why they are often referred to as utility tokens. Some tokens will be described later in this document, however, know that the ERC-20 standard ensures all tokens work with the same standards so things like transferring balances and interacting with smart contracts are all expected to behave in the same manner.

Denominations of ETH

Ether can be spent in as small a denomination as 10^18 (wei), which is 0.000000000000000001 ETHER.

    1 Ether = 1,000,000,000,000,000,000 WEI = 1 (EXA)WEI  
1 (MILLI)ETHER = 0.001 ETHER = 1,000,000,000,000,000 WEI = 1 (PETA)WEI  
1 (MICRO)ETHER = 0.000001 ETHER = 1,000,000,000,000 WEI = 1 (TERA)WEI  
1 (Nano)ETHER = 0.000000001 ETHER = 1,000,000,000 WEI = 1 (GIGA)WEI  
1 (PICO)ETHER = 0.000000000001 ETHER = 1,000,000 WEI = 1 (MEGA)WEI  
1 (FEMTO)ETHER = 0.000000000000001 ETHER = 1,000 WEI = 1 (KILO)WEI  
1 (ATTO)ETHER = 0.000000000000000001 ETHER = 1 WEI      

See the above diagram graciously taken from GWEI.IO. There are also nicknames for various amounts that are based on the names of computer scientists in the cryptography field. I highly encourage you to check out GWEI.IO for the full breakdown.

What is Gas?

Gas is used to pay transactions, it comes out of your balance of Ether and goes to the miners which record and confirm any transaction or contract interaction you make with your client. You can see the going gas rates at an eth gas station. You see at the time of this writing the rates were

Low Average High
16 min 45 secs 30 secs
12 gwei 29 gwei 37 gwei

When you use gas, your wallet or client will generally let you choose the transaction rate with an option like Low Avg High (or Advanced: set the Gas Price in gwei), so you can affect these values to adjust how soon you can see your confirmations.

Ethereum Smart Contracts

Ethereum has a Solidity programing language, which allows developers to make applications utilizing a concept called a contract. A contract is basically a published set of routines which allow for actions to occur such as sending funds or using them to back a loan for example. By reading about and understanding the contract, the public interfacing with it may have confidence in what the outcomes for each party will be. The operations which can be performed by the contract are autonomous, and generally require no human intervention.

You can browse a directory of smart contracts (referred to as dApps) at State of the dApps.

Various Use Cases for ETH Contracts

Compound/COMP

The Coinbase Earn program has a great tutorial on how Compound works. In the process they give you some to try the Compound Smart Contract out. The premise behind Compound is that you use a crypto asset to back a loan, and the person borrowing pays you a fee which you earn, sometimes as high as a 9-12% yield. See more about the Compound offer here:

Watch educational videos to earn Compound Tokens (COMP).

USDC

USDC is a stable coin by Coinbase. What this means, is that the price is kept at or near $1 USD. USDC is backed by USD and are always redeemable for USD. Another example of a stable coin is DAI, described below, which is part of the Maker DAO.

Maker/MKR

The Maker DAO is an Autonomous Decision making network, whereby holders of MKR (Maker Token) can cast votes on governance issues like what the stability fee should be for using the Oasis smart contracts to generate an asset backed DAI loan. Generally someone would be able to use the oasis app to save collateral for interest, draw on collateral by generating DAI, or conduct a trade.

DAI

DAI is the Maker DAO stable coin. It is pegged to $1 USD, and the mechanisms of the Maker ecosystem are set to enforce its stability. The Coinbase Earn program has a great tutorial on how DAI works as well. Start with any of the Coinbase tutorials linked on this website, and you will also gain access to learn about how to use Maker/DAI.

Golem/GNT

Golem is a network application built relying on users sending Golem Network Tokens (GNT) in exchange for gaining access to use your computer’s resources as a means to render Blender assets (3D graphics) or perform general computational operations. The beauty in this, is that you can earn GNT with spare CPU time on your old desktop if you want.