Elliot Waves is a fantastic topic which also supports fibonacci measurement
Elliot waves can be classified as A B C D E F
Its considered that price expansion ends at leg F
I will discuss about these in high to low mode as per screenshot.
1. Wave AB : Should be impulse
2. Wave BC : Should be minimum 0.382 of AB
3. Wave CD = Should go minimum 1.618 of AB
4. Wave DE = where E Should be always lesser than C
5. Wave EF = Final wave before price is ready to reverse
However just learning basics wont make you a good trader as price also makes double top and bottom and invalidate waves
An Elliot wave can be started from anywhere such as middle of trend, not limited to Tops and bottom but mostly on internet, people says it always start from top and bottom which is not true.
As long as the rules of waves are satisfied it can start from middle of trend too.
Example:
Harmonics waves and Elliots waves are similar but may differentiate in some conditions
In both Harmonics and Elliot waves a trader validates wave.
Validation Methods:
1. Fibonacci : A trader uses fibo to validate waves, Retracement and Expansion are two tools which is widely used by traders. Retracement for entering at pullback while expansion is used for reversal trading where a trader trades against the trade. Highly rewarding strategy, HFT and prop desk trader never trade pullbacks as they are scalper their main goal is accumulation and distribution where they hold for seconds and make enough which a common men doing job earns in a year.
2. Ratios : such as A to B, B to C, C to D and D to E
What invalidated Waves?
Rules. If rules are broken, a wave is no longer valid.
How to trade Elliot Waves?
You can trade in 3 steps
1. Structure Verification
Validate ABC minimum before taking actions on DEF, Do not trade at ABC
2. Ratios Verification
Verify Ratios after validating structure
3. Entry Verification
Entry should be verified by price action, Various tactics are used among traders which can be personal and may not be shared publicly. These tactics are like CHESS tactics where you have to trap your opponent
until he is check and mate, price will not move from your entry to TP. If your opponent i s check and mate then you can take entry. In other words they say price is taking stops or liquidity.
Example : 
4. Entry: Once you apply correct tactic, You can enter in a trade. Note that point
4. Wave DE = where E Should be always lesser than C
So Price may go just 1 pt below C and it still fall and wave will be valid but if your SL is incorrect then you will lose money, so rules are rules. if you are trading DE and selling at E,
You should put your SL above C only however this is just an example about how discipline is followed up by Elliot waves trader and its not same as shown on books.
