Step 1 : Do Operations within the Parentheses

3 - (6 + 8) x 3 = 3 - 14 x 3 = 3 - 42 = -39
The first operation to be done is always the one within the Parantheses.


Step 2 : Do Operations with Powers and Roots

3 + 2^5 = 3 + 32 = 35 (Here ^ represents powers)
3 + √ 16 = 3 ± 4 = 7 or -1.


Step 3 : Do all multiplication and division operations from left to right
Step 4 : Do all addition and subtraction operations from left to right

50 ÷ 10 ÷ 2 = (50 ÷ 10 ) ÷ 2 = 5 ÷ 2 = 2.5
If it is done from the other direction, you get a different (and wrong) answer.

Example you gave:

5 ( 3+6 ) -3 to the 2 power

Let's rewrite that as 5(3 + 6) - 3^2

^ = power symbol as someone already mentioned (I'm assuming here that you only power the 3, not the entire line)

First thing you do is parenthises (brackets), so let's do what's in the brackets.

3 + 6 = 9

So now the original line looks like:

5(9) - 3^2

Next thing to do is the power. 3^2 = 9 (3^2 means 3 squared.. in other words, 3 x 3.)

So now you have..

5(9) - 9

Next is multiplication

5(9) is another way of writing 5x9, which = 45

Now you have:
45 - 9

Now there's only one thing left to do..

45 - 9 = 36

..if that makes any sense.

Just follow that sort of order for everything you get, and it should work.