How do I prevent my weapon abilities from hurting my friends?

Simply Swords respects vanilla Minecraft teams. To prevent weapon abilities from damaging your friends, join the same team using commands such as:

/team add teamname
/team join teamname

Open Parties and Claims can also provide team relationships when it is installed.

How do I allow weapon abilities to buff or heal my friends?

Use the same team or party setup. Friendly effects recognise allies through the same relationship used to prevent friendly fire. Disabling PvP on the server also prevents player-on-player ability damage.