I need help with a translation
 

Would "are you going to eat that?" be "vas a comer eso?". That's what google translate says but my friend thinks that it would be "vas a comer esta".

The online translation is correct, except that there should be an opening question mark and a capital letter at the beginning of the first word.
¿Vas a comer eso?

Now, to your friend's point, if the object is known by both parties, and the object is feminine, then 'esa' may be used instead of the neuter pronoun 'eso'. 'Esta' means 'this (feminine object)'.

Thanks. I didn't put the upside down question mark because I don't know how to type that.

You're welcome.

There's an 'Accents' drop-down menu just above where you enter your posts here. You can use that to select all the special characters you'll need to type in Spanish.

The 'Accents' drop-down that Rusty mentions is the easiest method for you to use for now when writing something in the forums.

Whenever you decide that you want to be able to type those special characters while using other programs or web sites, go ahead and ask how to do that, or look for forum threads that discuss those issues.

Hmm, a note for myself and for others: at some point do we want to extend those threads with suggestions about how to type special characters on smart phones?