Summarize the following:
It's usually in the upper-right part of the keyboard.  It's usually on or near the J, K, or L keys. A heart (♥) symbol will appear where you placed the cursor. Even if the keys are unlabeled, the keypad will still work when Num Lock is on.
Click on the location where you want to insert the heart. Press NumLock. Press Alt. Press the small 3 on the virtual keypad.