First of all you need to know that the consensus model people used for very long long time was called Practical Byzantine Fault around the 1980 when these things took of and was essentially a computer science algorithm that helped a bunch of things come together and make conclusion based on the information they had.
Next up around 2009, we had a start up Bitcoin which introduced the Nakamoto era of consensus. Nakatamo created a shared proof of work mechanism which is many ways better than old Byzantine Model.
Finally in 2020, Avalanche launched it's Avalanche consensus model network. This things is complicated so I am going to attempt to give you a high level of understanding of it without setting up any of the engineers.
Now basically network follows proof of stake preety closely but it does have a few unique difference.
1) Subsample Voting :-
This means there's a large group of people who volunteered to participate in the network, and get randomly asked to check things. To put it in their own words small random subsets of validator are asked whether they think the transaction should be accepted or rejected.
2) Harder to Attack :-
Due to some technicality this consensus model is actually much more difficult to attack unlike -
Bitcoin - You were need 51% of all the computers to attack the network. Where
Ethereum - You were need 51% all the staked tokens to attack the network.
With Avalanche - You were need to control upto 80% of the network to perform an attack.
3) Transactions per sec
More than 6,500 transactions per sec and has finality clock of less than 3 sec. Compared to this Bitcoin 7 transaction per sec and an hour long finality. And even Ethereum palys to compare 15 transaction per sec and 10mins of finality.
In addition to being more efficient in this regards, the Avalanche network allows the blockchain developers to specify attributes they require their validators to have based on things such as geographical location for the purposes of abiding by regulation surrounding their fields of operation.
Likewise, validators can also specify which section or blockchain of the Avalanche network they wise to secure allowing for greater ‘ security customisation ' than its competitors.
So now I basically explain the how Avalanche consensus model works.
Conclusion:-
Avalanche was deliberately designed with scalibility in mind. With top tier payment processors like PayPal and Visa Avalanche has sub sec transaction times.