Press "ESC" during the game to pause it and bring up the pause menu in Spintires.
Options are:
Main Menu
Exit to main menu
You will be able to continue game
A confirmation prompt will appear before exiting.
Achievements
Track progress on your Achievements
Controls
View or change the Keyboard Controls
Settings
Change the main settings of the game including graphics and audio settings
Help
A short tutorial
Resume
Exit the pause menu and resume the game (or you could press ESC again to do the same)
Exit
Ext game
You will be able to continue game
A confirmation will appear