With previous versions of Raspbian you could edit inititab to make your Pi autologin to any account. Raspbian Jessie does not have inittab. The init system sysvinit has been replaced by systemd.
However setting Pi to autologin to console using pi user account is very easy. All you have to do is run raspi-config. You may launch this from a terminal session by the command.
Alternatively, from the Raspbian Jessie desktop, choose Menu → Preferences → Raspberry Pi Configuration.
If you launched raspi-config from command prompt it looks like below:
Scroll down to 3 Boot Options.
Select option B1 Desktop / CLI
Select B2 Console AutoLogin
Save and exit the configuration and reboot.
The Raspberry Pi will now boot to console everytime. You may setup a script to run at startup if you are planning to operate pi headlessly. To do this, edit /etc/profile. Each time a login shell is spawned all commands in /etc/profile are executed.
sudo nano /etc/profile
To execute a script /home/pi/myscript.sh, add the following line
Now everytime pi is powered on, it will autologin to pi user and execute your startup script, which presumably will take care of everything you it to do in headless mode.