I'm trying to get my head around it but one thing looks particularly confusing.
The article says that "If the second blockchain has agreed to be a Bitcoin sidechain, it now does something really special… it creates the exact same number of tokens on its own network and gives you control of them."
Does "the exact same number of tokens" mean the same exact amount in Bitcoin?
Therefore, does it mean that there's no exchange rate and you always move coins 1:1 between Bitcoin and a sidecoin?
This doesn't make much sense to me. How does the actual currency amount get converted from BTC to a sidecoin?
There isn't any "sidecoin" here. One of the slogans for sidechains is "altchains without altcoins". The idea is that you are in some sense still using bitcoin tokens, even though you're doing so in an unorthodox way.
It can be implemented either way - it's up to the sidechain. For example, a simple sidechain might lock its exchange rate at 1=1 to the bitcoin network (if the creator just wanted to test out protocol improvements, such as faster block times).
On the other hand, someone could create something totally different, like a lotto coin, where each week one of the holders is allowed to "withdraw" all bitcoin in the network back to the bitcoin blockchain.
All that matters is that all the miners/participants in the sidechain agree what the rules are for importing and exporting bitcoin. If the sidechain miners allow the withdrawal to go ahead (and it reaches enough confirmations to mitigate a double spend attack), then the bitcoin blockchain allows the original coins to be unlocked.
The article says that "If the second blockchain has agreed to be a Bitcoin sidechain, it now does something really special… it creates the exact same number of tokens on its own network and gives you control of them."
Does "the exact same number of tokens" mean the same exact amount in Bitcoin? Therefore, does it mean that there's no exchange rate and you always move coins 1:1 between Bitcoin and a sidecoin?
This doesn't make much sense to me. How does the actual currency amount get converted from BTC to a sidecoin?