You can use either First or Firstly(or Second, Secondly) to number your points. “First” and “second” are more common than “firstly” and “secondly”.
First, I would like to thank everyone for coming today.
Second, I would like to congratulate the bride and groom.
First, Second, Third, Fourth, etc is the most common way to number your points when you are speaking or writing in English.
We number points in this way when we want to put some order to what we say or write. Number points like this is more common in essays and not common in informal speech.
Firstly/Secondly/Thirdly is also generally accepted as correct but be careful as many people will criticize you for using these forms as being overly formal.
If you do decide to use firstly and secondly, make sure not to mix first, second with firstly, secondly.