Though the triangle doesn't really resemble a bottle of bleach, try to remember that it represents one. You may bleach as needed, using either chlorine or oxygen-based bleach on the garment. Use non-chlorine bleach only if the symbol of a triangle has diagonal lines in it. Chlorine bleach leaches dye out of fabrics, so it is typically only used for white fabric. Non-chlorine bleach is oxygen based and shouldn't stain or ruin your clothes. That goes for both chlorine and oxygen-based bleach. If you have a stain, try using another method to remove it.

Summary:
Bleach your garment if the label contains a triangle. Identify what kind of bleach to use. Do not use bleach if the symbol of a triangle has an X through it.