First, you must install the Play Store on the device. You can find download links here. Use the file manager that comes in the stock firmware to browse to the file that you downloaded (Probably under MyFavorites) and install it. You may need to allow untrusted sources.
Once you have the Play Store installed, sign into your Google account and download and install Nova Launcher.
After Nova Launcher finishes installing, press your home key. You will be prompted to select a launcher. Tap on Nova and select just once or always, your pick. I find Nova to be pretty easy to use on the Omate TrueSmart.
Once you're at the Nova home screen, press and hold on a blank spot on the screen. A menu will pop up. Choose Shortcuts
Scroll down and find the entry for Settings to expand the list
Scroll down further until you find the 2 entries for Sync. Choose the second entry
You will now have a Sync icon on your screen. Select this and now you can choose accounts.
Once you choose an account you can change the sync settings for that account. If you want to delete an account, swipe from the left edge of the screen to the right to bring up the menu. From the menu you can remove the account.