Yes you can.

"Not only" means literally "pas seulement" in french.

Je ne mange pas seulement des pommes

Is correct. But if you don’t use the "mais" (meaning "but") after it, it is correct, but we are usually expecting something behind it.

Je ne mange pas seulement des pommes mais aussi des bananes

Je mange non seulement des pommes mais aussi des bananes

Is correct too, it insist on the fact you don’t eat only apple.

Je ne mange pas que ça

Doesn’t need something behind it, but you can say :

Je ne mange pas que ça, mais aussi ceci

Correct too.

ça ne sert qu’à ça

It is not ce but ça. The rest is correct.

If you want to understand the meaning of non, this question might help you !