1. Friends
It would be so lonely without any friends wouldn't it? xD
What are friends for?
If the person is on your friend list, you can easily message him via the Friends section. You can also check on his formation anytime.
Having at least 16 names on your Friend list will also unlock the maximum morale boost for "Many Friends". So be sure to make friends! xD
How to add friends?
You can click on "Add Friend" in the Friends section to search for a friend if you know his IGN. (Provided the game does not crash on you.)
You can also add a friend from the arena if you click on the player's banner.
In Nation War, the 'Add Friend" option is available for all ships within the same camp.
2. Enemy
When you check your news feed and see that a player has stolen your skill fragment, or he has beaten you in arena, chances are he might have become your enemy, and his name will appear on your Enemy list in the Friends section.
If a player is on your Enemy list, it means you have him 'marked down' in arena. You should be able to challenge him anytime, even if he gets a little too far ahead in rankings (this has limitations of course).
So for example you need to break into Top 10 for a morale boost and you have someone already in Top 10 willing to help you and be your stepping stone. However, you are still not ranked close enough to challenge your friend yet. :'( Here is what you can try out, get your friend to steal one of your skill fragments to get himself on your enemy list (your levels must not be too far apart in order for him to be able to steal your fragment). If successful, you should now be able to challenge him in the arena! However, this will not work if your friend is ranked top No 1.
After a while, the player will cease to be your enemy. It could be that a certain amount of time has lapsed, or new enemies have replaced the old ones. I am not exactly sure of the exact conditions so if you have any info do let us know! :)
3. Follow
I have always wondered what is the use of this function, and never really understood it till I saw the official guide on DP3D here.
Basically, it allows you to mark a player on your Enemy list forever! Yep forever, until you decide to remove him from your Follow list. So once you stalk... eh, I mean... follow a player, he will always be your enemy until you un-follow him.
To follow a player, click a name on your Enemy list and click 'Follow'.
The number of players you can friend or follow all depends on your VIP and Captain's level.