"恭喜" means "congratulations" in Chinese. To say "congratulations" in Chinese, you can simply say "gōngxǐ" (gong1 xi3).
Here's how you can use it in a sentence:
"Nǐ zhènglì le yīgè wánměi de chéngjī, gōngxǐ!"
Which means: "You have achieved a wonderful accomppshment, congratulations!"