Shabbat question from a newbie

Am I correct in that lighting the Shabbat candles is 18 minutes before sunset?

Does everyone adhere to this time frame?

Also, does it matter what type of candle is lit? Or how many?

Sorry for these questions, I am just beginning my journey into Judaism, I was born Jewish parents, but they did not raise me in the faith.

My aunt passed away this week, she was the matriarch of the family, and very active in her faith. She would always send me a Shabbat Shalom message and tonight I would like to light candles in her honor and begin the tradition.