JULIE'S HOMEWORK:

We celebrate Christmas by singing carols and decorating Christmas trees.
On Christmas day, I always found nice gifts under the Christmas tree.
I can eat roll cakes and chicken.

CORRECTION:

We celebrate Christmas singing Christmas carols and decorating the Christmas trees. On Christmas day, I always find nice gifts under the Christmas tree. I can also eat roll cakes and chickens.

EXPLANATION:

1. It's more appropriate to use "Christmas carols" than "carols" in your first sentence.
2. Don't forget to use determiner "the" "a" and "an" if needed in your sentence.
3. Please use "find" rather than "found" because you are narrating the things that you usually do every Christmas. You don't need to use past tense.
4. Please use the plural form of chicken on your last sentence because practically saying you won't just consume one chicken. We make it plural to be parallel on the other noun that you have which is "roll cakes."^_^

COMMENT:
Hi Julie!
Thank you for sending me your homework. Your sentences are all almost correct. You just commit few minor grammar lapse. I hope you'll take note and remember all of the things I corrected and see you again on Tuesday. Have a nice Sunday night.
-Teacher Joanna