To select multiple messages to archive, click the command key (Mac) or the control key (Windows) while clicking each message you want to select. You can also use the same key command to deselect a message.
To select all messages, click the command + A keys (Mac) or the control + A keys (Windows).
To select a range of messages, click the first message you want to select, hold down the Shift key, and then click the last message you want to select. All messages between the first and the last messages will be selected.