to answer all your questions you use the IRS form 1040.
www.irs.gov
well it does count as income. And you should be taxed, although many people consider e bay under the table. A LOT of people do not pay taxes on their e bay stuff.
you can put it on your annual tax thing (1040). (the IRS sends you it)
Taxes for this year (well last year) are done (was due April 15th)
you send whatever you owe to your local IRS place (usually the capitol of your state)
you get refund/or pay every 1 year (JAN-DEC is a one year cycle)(and the form is due April 15th)
I get $7 back this year (whoo~)
I had to pay $50 last year because of income I made that wasn't from my job
( a bank account that i was earning interest on)
there is a section for "other income".
however I suggest if you do this keep a record of everything you donate ect because you also get a tax refund. If you work and have a job you should also include your w2 ect.
Sales tax in general on e bay you don't charge unless they live in the same state as you. State sales tax and general income tax is different