I'm not going to say where it fits in the timeline because I don't know (no one knows besides some guys at Nintendo).

you can play them in either order and Nintendo has not stated which one comes first in the timeline (that is if there is only one timeline)

OOA:
-triforce tells link to go to labrynna
-link meets impa
-they meet Nayru who can control time (years)
-impa is possessed by an evil spirit (Veran)
-Veran captures Nayru and messes up time
-link goes to Maku tree
-Maku tree dies
-link travels back in time when Maku tree was still alive
-link needs to collect 8 essences of time to restore maku tree
-link travels back and forth in time collecting the essences
-Ambi the queen of Labrynna gets possessed by Veran
-Link defeats Veran
-Link travels to Subrosia (can be the other way around too)

OOS:
-triforce tells link to go to Subrosia
-link meets Impa and Din
-Din is the goddess of the seasons
-Onox appears and f***s everything up
-seasons get messed up
-link meets Maku tree
-link needs to collect 8 essences of nature
-link needs to make use of seasons to collect essences of nature
-link uses rod of seasons (which gradually becomes stronger) to change seasons
-link defeats Onox
-seasons change to normal
then:
if OoA has not been finished
-Link needs to go to labrynna
if it has been finished
-Twinrova capture princess Zelda
-flame of sorrow , destruction and despair are lit
-ganon gets revived
-link defeats ganon
-link uses boat or raft to return to hyrule

Now I always figured that Link's Awakening came after the Oracle series because of the specific 'link uses boat or raft to return to hyrule' ending. But alot of people would argue about that.

Also...

play the games!!