Bitcoin Forum

I don't really know what a fork is, could anybody explain?

As bitcoin is open source, anyone can copy the original and make some changes on it. So the original one and this second one would have the same origin but would end up being two different coins. This is what is happening now: some people believe that bitcoin needs some specific improvements and create a new fork.

The problem is that bitcoin is based in blockchain technology so people who use blockchain have to support one fork or the other.
Last fork gave birth to Bitcoin Cash but as you can see the original Bitcoin remains the most supported one.

Bitcoin rely on their blockchain to keep their data.
The blockchain stays on many computers - everybody having bitcoin qt installed will download the whole blockchain (and most keep a local copy of it).
For whatever reason - intended (software change) or unintended (rogue miners, bugs, attack) the blockchain can split (fork).
This means that while blocks 1-x are identical, there will be 2 blockchains, one with blocks 1-x and then y1, and another with 1-x and then y2.
In most cases forks are short lived - you will not know it happened - and one chain is not used by anyone.
In some cases, like it was the birth of Bitcoin Cash, both forks (both versions of the blcokchain) exist, but they behave now almost like 2 separate blockchains.

And how does a fork work?

Since Bitcoin works by keeping a ledger (records of who owns how much money), a fork is simply a copy of the ledger.
They will copy the old Bitcoin ledger (blockchain) and use it independently so that two ledgers become more and more different over time.
Think of it as some bank coming to the bank you are using, copying your balance and offering the withdrawal of it in their own bank, except that the money you withdraw at this new bank is different money, different currency and does not hold the same value.
This is an easy way of getting customers for your new bank.

If you want to learn more about it in a technical sense, you will need to read about blockchain technology.

And what can I  use a fork for?

It's basically a new coin, whose past up to a specific date is equal to the forked coin.

To put it less technical, a fork can occur a proposal to update the rules of the network is made. In this case Segwit 2X wants to allow for blocks with a maximum size of 8MB (in theory), among some other things as well (the other things are quite controversial and I want to keep this post as unbiased as possible). So at a certain block number the supporters of 2X want all the miners to start signalling segwit2x but that's not likely to happen so blocks with mined by the segwit 2x software will get rejected causing a split of the chain.
This is totally my understanding of what a fork is, I am not an expert.

Well it is not a tool, it wasn't intended to be 'used' for something. It just happens. Someone wanted to go their own way, so they did.
You can join them, you can ignore them, you can protest them, you can buy their their coins if you think they will increase in value or be useful to you, you can sell the coins you got by them copying the ledger if you think their coin will decrease in value or is useless to you.
Fork is an event, you can plan accordingly.

Its exactly like a fork in the road. There is a single chain and at a certain point it breaks into 2 and each side goes a different way (if were talking about contentious forks). If you owned coins before the fork, you will have them on each side of the fork. Hard forks are done to change the base layer of the coin, while soft forks change less ingrained properties.

like a token or not?

A token is something that runs on the top of a proper coin's blockchain.
So since a token has no blockchain, "fork" and "token" can't really belong to the same sentence imho. (So no, it's not like a token.)