TDS by Client

Dear Friends,

I am a new member of this forum and anticipate to learn a lot from you. I have some preconcieved notions about taxation in India and would request you to guide me.

1. I understand that TDS is a kind of income tax or TDS done only for the income tax.
2. I am a free lance professional and I conduct workshops. I have a vendor-client relationship with different companies. My question is "Does a client has right do a TDS from the billed/invoiced amount from the vendor?, If yes What are the documents they need to privide to the vendor along with the payment? How can a vendor (myself) would claim for a return if Tax deducted as TDS is more than the actual liability for a financial year?"
3. I am an individual professional and have PAN. Do I need to have a TAN also?

I would appreciate if my friends could help me to have a clear idea.

Thank you,

Partha Sarathi