Loops

For

for i = 0, 20, 2 do
    print(i)
end

Notice how there are 3 values.

Starting value
Ending value
Add to i by

The last number which determines the amount of addition is optional.

While

while num < 50 do
    print("hi")
    num = num + 1
end

block scopes usually end with end keyword.

Another Variant

n = 50
repeat
    print("hi")
    n = n - 1
until n < 20

Very similar to do while from C but only difference here is that the condition needs to be false.
If the condition is true, it will run once and exit.