I am relatively inexperienced in PL/SQL and hence I need help

I have two tables like this:

GC_COUNT

FID CID ANNOTAT
____________________________
1 1 1, 1-5
1 2 2, 2-10
1 3 3, 10-15
2 1 35, 1-4
2 2 45, 3-5

All varchar and the combination of FID and CID is unique.
For each FID the application might generate any number of CID's.

What I need to do is write a trigger after an FID is inserted into this table which will capture the ANNOTAT of all CID's for a particular FID and concatenate them and update another table like this:

GC-CBL

FID ANNOTAT
__________________________________
1 1, 1-5 2, 2-10 3,10-15
2 35, 1-4 45, 3-5

Here FID is the PK.
Thanks for all hekp rendered.

Nizar