How do I volunteer to help in a disaster?
It's great that you want to help people affected by disasters. Other than reading about them to understand where the key needs are, you should become familiar with what kind of contributions will be really useful. Interaction's guide will be a good place to start.
Given the urgency, positions for rapid deployment typically do not appear on ReliefWeb. You should look for organizations working (or planning to work) in affected areas and see if your skills might be a good fit.
Want to be an online volunteer? See Ushahidi's guide.