It's rare to find a web hosting provider that offers free trial periods, but luckily, money back guarantees are common. Typically, web hosts will allow you to sign up and purchase a plan, and if you find that what you bought isn't the right option for you, you can take advantage of the money back guarantee to receive a full refund of the fees you paid.
Many services offer so-called unlimited or unmetered service for whatever amount of bandwidth, disk storage and sites you use. It's important to understand that most terms of service actually do limit the definition of "unlimited" to what's considered reasonable use. The bottom line is simple: if you're building a pretty basic website, unlimited means you don't need to worry. But if you're trying to do something excessive (or illegal, immoral or fattening), the fine print in the terms of service will trigger, and you'll either be asked to spend more or go elsewhere.