Blocking a player in the Global Chat means that you cannot see messages sent by the blocked player. Please note that this is not the same as the Report function, which sends a report of the player to the developers of the game.
Continuing to interact with any player who is unpleasant to you is by your own choice - you can block another player to ensure you don't have to read anything they write.
You can Block players by pressing their name in the Global Chat and then selecting "Block". Blocked players can be unblocked from the Settings menu by pressing the "Blocked Players" button and then selecting the player you want to unblock from the Blocked Players menu.
If you wish not to communicate with other people or find the whole chat unnecessary, it can be hidden by tapping the speech bubble.