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urdu....والا

it is a very big answer and i will try to cover all the topics(i i will fail certainly but i will give it a try)

wala is generally used to denote a person(or a noun) and it is it is the doer of particular thing or it associated a particular thing.

ex. dene wala - giver or 'the one who gives'
karne wala - doer or 'the one who does'

karna to do; dena to give

the above examples can represent a person or a situation both
ex. 'pareshaan karne waala bayaan' means upsetting statement.
'pareshaan karne waala aadmi' means annoying/irritating man

the other case

feriwala - hawker
doodhwala- will mean a dairy farmer or who sells milk.(doodh - milk)
etc.

kabuliwala is a famous story written by rabindra nath tagore, here wala denotes the origin of the 'person'(kabul afghanistan)


apart from that i dont know about the same usage in pakistan but as far as my hindi urdu contacts go, all understands it when i say
"main aane waala hoon"
means i will come

"kab jaane wala hai" -when will u go

here the usage is same as aaunga or jayega respectively.

another ex.

mehmaan aane waale hain -guests are to come or guests will come

we are talking of future here.
but u cannot actually always replace jayega with jaane wala hai kind of sentence. there is a subtle difference in expressing future. and there is a difference, and of course the original meaning 'the one',
ex.

wah padhne wala ladka hai
he is a studious boy

apart from these there is another usage which is for past tense

ex.

list interview ke baad lagne waali thi

here we are talking of past tense about action interview and list lagna(display of list) happens i.e.

the list was to be displayed after interview


u get some idea now i suppose.