Dungeons & Dragons is normally played in a tabletop environment where everyone meets in person, but we have D&D games running in one section of an online Forum environment with people from all over the world. The site, International Discussions, allows everyone to participate according to their time zone and abilities.
It is very easy to get started. You just
Join for free, introduce yourself and then create your character. Nothing to download, nothing to pay for.
You are not required to make any special posts or have some special activity level but you should be active enough that players can expect your input. There is more than one D&D Scenario running so you can choose which one you want to join in.
Dungeons & Dragons PBP RPG