need help with nodes

hello pro blender users, i am trying my best to learn nodes to create materials and textures and everything i can in it,for a first,am sure for any one who is a pro will think its a silly question,but what is a vector (blue, purplish dot)mean in nodes? and second, is there a good website for video tutorials for nodes and textures that go over everything for nodes starting with the beginner stuff and that they go over every single one from the add on list in the nodes drop down menu(shaders, mixers, glossy,etc) and how to be a pro in using them? thanks :frowning:

Claas have a many good tutorial that i goes really slow and gives the time understand for example this and some other on is Youtube channel and active member is as well.
The secret to understand all this is to try it yourself and if you have a specific question then you can ask here or in any forum of your choice.