Can I have two visas to USA at the same time?

Well, what happens is that you have a 10-year B1/B2 visa and then you decide to come to the United States as a student on a F1 visa or get a job offer on H1 visa.  In some cases, the consulate may cancel your other visa by making a note in the passport or by notifying you officially by mail.  However, it may leave it alone as well.  So during the validity of F or H visa, you will be admitted using them, and you need to make sure that it happens when you meet with the immigration agent so that you have enough time to stay and it is in compliance with the terms of your visa (e.g. if you are admitted under the visitor visa, you will be unable to work, even though you have a work authorization under the H visa).

If you never overstay a visa, when one visa expires, you are free to use your tourist visa to visit the United States.  If for some reason your tourist visa was cancelled and you now want to visit the US again, as long as nothing else has changed dramatically in your life, you should have no trouble receiving a new visitor visa.