Open chat interface, click the "Add Friend" icon, and then left click on a player nearby to add him/her into your buddy list.

Inspect buddy info
Right click on a player in your buddy list to inspect his/her basic information, including race, gender, nickname, ID, level, etc.

Review mail history
Right click on a player in your buddy list and then click "Mail history"in the interface that pops up to review your chat record with him/her.

Guest
Right click on a player in your buddy list, click "Acquaintance" to put him/her into your guest list. Guest info will be deleted when you log your character out of the game.