When you install SQL Server, you need to choose accounts for SQL Server services. Here are some usefull links that can help you to make a correct decision:
- Configure Windows Service Accounts and Permissions
- Server Configuration – Service Accounts
- Guidelines on choosing Service Accounts for SQL Server Services
- Service Accounts Step-by-Step Guide
As overall installation manual you can use Jonathan Kehayias’ guide described in his post SQL Server Installation Checklist.