Basic ones like Plus (same as addition), Minus, Equal, Percentile, Multplication (represented by an asterisk), Number Sign should be on your keyboard, look where the "number" keys are located, just below your function keys.
Its possible some of them might be embedded keys located with in other keys, this means you have Press Fn + the key where the sign is also located.
Some complex symbols like Division can be found in Character Map:
Click Start, type: character map
Hit Enter on your keyboard
Click in the Font list box
Scroll down and select 'symbol' as the font choice
There you will see a gallery of symbols, multiplication, division and many others.
Select the one you want, click copy.
Open the program you want to insert it in such as your word processor (Microsoft Word) then click Paste (CTRL + V) Thats it.
If you are running Microsoft Word 2007 or later installed, you can access this from the Insert (tab) > in the Symbols group.