how do i install it on my phone once i have downloaded the .apk file onto my computer.
You're better off downloading it straight to your phone.. But to do it from your computer... plug your phone into your computer. Mount the SD card, drag the apk to the root (main section) of your SD card. Unmount the SD card. Using an app like Astro File manager or File Expert, go into your SD card and tap the apk and install it.