what information i need from host provider before to buy domain,
what companys are relayable.

If you are talking about registering a new domain name, then nothing. You may need your hosting company's server info (e.g. ns.nameslave.com 207.155.127.155 or something like that) but you can always modify it AFTER your registration. Hope this helps.

Just be sure to register the domain to your own name and not to your hosting company's name. Otherwise you may have troubles later (moving to another host, transfering domain, etc.)

5 minutes and no-one else can have your domain name. Within 5 minutes of registering a new domain name, your domain name will have been entered into the Internet Domains Shared Registry and will no longer be available to anyone else in the world.

You do NOT have to use it straightaway.

Just specify the hosting company's name servers when you register. Or if you don't have a web site or hosting company yet, add them at a later time using your online domain control panel. Contact your hosting company if you don't remember the names of its domain servers (two are required).

there are many registrar to choose from.

I would never have a hosting company register my domain for me. Some not all hosting companys look out for there own best interest when it comes to registering domains for thier customers by registering the domain in there name making it difficult for you later if you decide to swith host.

Yep, sometimes it will just be the admin contact, sometimes the whole registration will be in their name - it seems especially if the domain is included in a package with hosting. Good marketting ploy targetted to newbies that don't know better, I have to admit.

With Godaddy.com and the rest, it's just not worth the grief to go elsewhere. $9 or less for a year, it's yours. And with Godaddy and others, you can set it up to point at a parked page at the registrar for free usually. So you can take your time setting things up.

-WC-