To add symbols you should use a combination of two keys : ALT + “NUMBER”
where “NUMBER” is a key (number) from your numeric keypad.

For example, if you want to insert a heart symbol you should:

1. Make sure your keyboard is in NumLock mode and you are using the numeric keypad. If you are a laptop user your numeric keypads are usually the numbers in red.

2. Hold ALT key and press 3.

3. Release the ALT key to insert the heart symbol.

A list of other symbols you may want to know is:

for ☺ 1
for ☻ 2
for ♥ 3
for ♦ 4
for ♣ 5
for ♠ 6
for • 7
for ◘ 8
for ○ 9
for ◙ 10
for ♂ 11
for ♀ 12
for ♪ 13
for ♫ 14
for ☼ 15
for ► 16
for ◄ 17
for ↕ 18
for ‼ 19
for ¶ 20
for § 21
for ▬ 22
for ↨ 23
for ↑ 24
for ↓ 25
for → 26
for ← 27
for ∟ 28
for ↔ 29
for ▲ 30
for ▼ 31

This should work in any text editor, browsers (facebook, blogs, email), IM (live or yahoo messenger) or office.