Recovery-Mode / Hard Reset
While switched off, keep the following buttons pressed. Release the power-button once the Samsung Galaxy W(I8150) is switched on and keep pressing the Home- and Volume Up-button.
As soon as you see the Android with the box, release the Home- and Volume Up-button.
After you hit the menu-button shown on the last image, the screen will gray out, you will have to wait until the recovery menu appears.
-reboot system now
Reboots the system.
Install diverse updates like themes, custom roms etc.
-wipe data/factory reset
Deletes all the apps, data and system settings(Files on the external SD-card will stay untouched)
-wipe cache partition
Only wipes (formats) /cache partition (sometimes used as temp storage for updates, market downloads, etc) it hasn't anything common with Dalvik-cache which is in /data by default and it implies that the following boot after wiping cache partition will not be any longer than usually.