Hi!.... Logging a find is really quite easy! Just navigate to the Cache page you originally found the coordinates on. In the upper right corner of this page is a 'log your visit' icon. Click that icon and follow the instructions. You may log 'finds', 'did not finds', 'notes', etc.
Many cachers like to tell a little about their experience finding the cache, what they liked/didn't like about the hide, weather, etc., etc. No real rules here. Some tell what items they traded if any. Common abbreviations you might see are: TNLN: Took Nothing/Left Nothing, SL: Signed Log, TFTH: Thanks for the hunt.
Have fun! Happy Hunting!
JScott98003 in Seattle, WA
PS... you may also add photos you may have taken on your hunt. Check out the 'Visit The Gallery' link that appears right before the cache logs.
PPS... My first post to a forum here... appropriate for your first also!