I'm completely new. I'm new to FFXIV, I'm new to MMOs, I'm new to healing and general MMO battle tactics, so I wondered if I could reach out for some help.

For background (so you can judge your answers by my 'skill' level): I get that I'm in the group in order to keep everyone alive, and I need to concentrate on both me and the tank predominantly. I know that spamming cures just gets me hurt (and that helps no-one) and that I'm not there to deal damage unless everyone is healthy and I don't have to worry about attracting enmity.

Then I got the Repose ability and it has changed things up. I can sleep things to deal with later. Which is good. I get that to help our DD colleagues I should tell everyone and mark the target.

I guess my question really is - when should I use this ability, and what enemy should I choose to use it on?

tl;dr - when and on whom should I use Repose?