If I want to buy a hosting do I need to wait to the beginning of the month? and if I don't is the payment any different?
yah you can buy hosting.. setup your DNS on the host and have your website online in hours if your dealing with decent providers. Well even the crappy providers can you get online fast... might just be a small wait to get your domain name registered
Yeah, as mentos said, you can buy hosting anytime. Pretty much all hosts bill on the day you start the account. Some hosts will allow you to change your due date after signing up if you need to.