entries in one cell separeted by coma

Hi!

Is it possible to be simply done?

I have a column of letters, but sometimes two or more letters in one cell, like:

1 a, f, g
2 a
3 a, b, b
4 a, b, c

I would like to have somewhere else a column of all the letters (don't care about repetitions):

1 a
2 f
3 g
3 a
4 a
5 b
...... and so on

And also I would like to be able to find all cells that contain a specified letter, ex. a

I was trying to do that for a while but no luck
I would really appreciate someone's help!