your going to have to ask a more specific question. some people here have textbooks worth of information on tubes in their head. they arent going to type a textbook worth of information for one person to read on a forum. i's suggest reading some books/sites that talk about tubes and then ask questions on what you've read. this will get you much more meaningful results.
The Guitar Amp Handbook: Understanding Tube Amplifiers and Getting Great Sounds by Dave Hunter is a great book to read to understand the basics, circuits and how it all effects the sound. there may be some useful websites for your level, but i dont know of them as i read that book for my basic knowledge.