I am not sure I understand fully about speed running I do watch a lot of videos but don't really understand do I need a certain seed, how do people find obsidian like they know where to go?

Welcome to the site. I assume you ask about Minecraft? game specific questions you should ask in the game forums, in this case: https://www.speedrun.com/mc/forum. There are also lots of guides you can read there, which might answer your questions.