To start, stop, pause, resume, or restart the an instance of the SQL Server Database Engine:
- On the Start menu, point to All Programs, point to Microsoft SQL Server 2012 , point to Configuration Tools, and then click SQL Server
Configuration Manager. If the User Account Control dialog box appears,
click Yes.
- In SQL Server Configuration Manager, in the left pane, click SQL Server Services.
- In the results pane, right-click SQL Server (MSSQLServer) or a named instance, and then click Start, Stop, Pause, Resume, or Restart.
- Click OK to close SQL Server Configuration Manager.
From: Microsoft - Start,Stop,etc. SQL Server
You can also do this from within SSMS:
In Object Explorer, connect to the instance of the Database Engine,
right-click the instance of the Database Engine you want to start, and
then click Start, Stop, Pause, Resume, or Restart.
Edit: As Lamak mentioned, within the SQL Server Configuration Manager you can change all the services StartMode to "Manual" so they do not start on boot.