Amidst the massive wait times experienced by overpopulated World of Warcraft: Classic servers, Blizzard is giving players the opportunity to transfer their characters to less populated realms where they won't need to wait hours just to play the game - and it won't cost them a penny. Many of these realms were created during the game's launch in order to remedy the fact that so many people were sitting at their computers waiting for a chance to log in.
Now, you'll be able to move your character to a less populated realm where you won't have to wait and you'll still maintain all of the progress you've made on your current realm. Unfortunately, you'll need to convince the friends you've made thus far to transfer realms with you at the same time, otherwise you'll no longer be able to play with them. You can still contact each other if you exchange battle.net usernames, though.
In a recent update, Blizzard explained the requirements to change realms and announced that players will only be able to make this change during the upcoming weekend. However, you won't be able to transfer your character if they are the leader of a guild, they have an auction in the auction house, or they have unopened mail. You can make this transfer from the character selection screen, but it can take up to a few hours and the transfer may not process if the destination realm becomes full.
On top of that, you can only transfer a character one time. Once they arrive in their new realm, that's where they're staying. You also may be required to change your character's name if the destination server already has somebody with the same name. Finally, you cannot transfer a character to a PvP realm if you already have another character of the opposite faction in that realm.
Although it's nice to see Blizzard taking steps to alleviate some of the absurd waiting times caused by overpopulated servers, giving players a very limited window and a handful of stipulations to change their realm probably isn't the greatest long term solution. If you are able to make a realm change though, it's definitely recommended to avoid long wait times.