Unless you're high up in the executive ranks or have a skill that's in especially short supply, it's unlikely you'll be asked to sign an employment contract in connection with your next job. Instead, you'll probably receive an offer letter that confirms, in writing, your prospective employer's intent to hire you and outlines the terms of the job.
Offer letters are important for several reasons.
First, they are quasi-contractual. They usually state your job title and salary and, often, some of your duties and the benefits you will receive. That's why, for example, if you are promised things orally during interviews, insist they be included in the offer letter. For example, if you were promised three weeks' vacation instead of the standard two, make sure the longer period is spelled out. A personal experience illustrates the point.