Verses 6-12 repeat for a second time and give more detail about how Noah went into the ark with his family and the animals in Genesis 7:1-5. This is not a new event.
In the six hundredth year of Noah's life
"When Noah was 600 years old" (See: rc://en/ta/man/translate/translate-ordinal)
the second month, on the seventeenth day of the month
Since Moses wrote this book, it is possible he is referring to the second month of the Hebrew calendar. But this is uncertain. (See: rc://en/ta/man/translate/translate-hebrewmonths and rc://en/ta/man/translate/translate-ordinal)
on the same day
This refers to the specific day when the rain began. This phrase emphasizes how all of these major events happened quickly when the time arrived.
the fountains of the great deep burst open
"water from under the earth rushed up to the earth's surface"
the great deep
This refers to the sea that was thought to be under the earth.
the windows of heaven were opened
This refers to rain. It describes the sky as a ceiling that keeps the waters above it from falling down to the earth. When the windows, or doors, in the sky were opened, the water came down through them. AT: "the sky opened" or "the doors in the sky opened"
If your language has a word for a great amount of rain, it would be appropriate here.