I just don't understand why we using square brackets on dict[char]

Question

Letter Counter
Given a string as input, you need to output how many times each letter appears in the string.
You decide to store the data in a dictionary, with the letters as the keys, and the corresponding counts as the values.
Create a program to take a string as input and output a dictionary, which represents the letter count.

answer:
text = input()
dict = {}
for char in text:
dict[char] = text.count(char)
print(dict)

Answer 1

With the square brackets, we we access the value of the key:
dict[key] = value

You may want to review the lesson about dictionnaires in the sololearn Python course