index expected, got nil

I need help with tables, I want to insert a value into a table that exists within a table.
for example:

a = {}
a[1] = {x = 5, y = 4}
print(a[1][x])

gives me just a blank space.
Is there any way of me inserting like so without using textutils.serialize?
I got an error for a code I was using

a = {}
a[1][x] = 5

and it said "index expected, got nil"

local a = {}
a[1] = {}
a[1]["x"] = 5 -- OR:
a[1].x = 5

It needs to be a table in short

THANK YOU!!! I could've found this out myself, although I was kinda lazy, but this didn't just help me with the script I had a problem with, now 3 different things that are really complex are extremely more easier to understand for me!!!