Could someone please explain to me what a delimiter is?

Answer 1

if your string is as below :

asd,sdf,hjk:qwe,Yui

your delimiter , would give you below sub string from input string :

asd
sdf
hjk:qwe
Yui

if your delimiter is : below are substrings :
asd,sdf,hjk
qwe,Yui

if your delimiter is s then below are sub strings

a
d,
df,hjk:qwe,Yui