Advice on contract

Hi I am small labour person earning day to day. I want to make a contract to a Web Developing company to build a website for me with all the specific requirement which I want for my website. I dont want my idea for website should be disclosed or leaked apart from to only I am giving this contract.

I don't know how this contracts are made, whom should i contact to make this agreement, how much will be the cost?

I appreciate your time. Looking forward for your earliest reply.