It is easy to add a lot of shapes and symbols to your work on a Mac. Just as quickly as I can type a string of letters, I can also add ∅ ➜ ☝ ♘ ÷ and others. But even though it is easy to add them, it certainly isn't easy to figure out how to add them!
The first step using these characters is to head to your System Preferences. Once you get there, open the Language & Text preference. Look for your Input Sources tab at the top. There will be slight differences in how that looks depending on which version of the operating system you are using, but it should look similar to this...
The key things you want to check for here are...
Your input methods should already have "US" checked since that is your default language.
You will want to add to that a check mark that will show the Keyboard & Character Viewer.
Make sure the box for "Show Input menu in menu bar" gets checked.
You do not need to check the Unicode Hex Input box.
Now close your Language & Text preferences and return to your Desktop.
Now you should see an American Flag up in your menu bar. That will give you access to your Character Viewer.
So go ahead, click the flag, and choose Show Character Viewer in the menu. And now you'll see something like this...
In the left-hand column, you will see a lot of different choices - Mathematical Symbols, Number Symbols, Arrows, etc. All of these can be added to any of your documents. Just click the symbol the symbol you want (above I've clicked "white sun with rays" and click the Insert button in the lower right corner. That puts the symbol where your cursor is in your document.
And you can do that as many times as you want with any symbol you like.
ADDITIONAL NOTE: If you have an older version of OS X, you may find the Character Palette checkbox in a different location. Rather than looking in the Language & Text control panel, check in the International control panel. Click on the tab for Input Menu. Then you can turn on the Character Palette.