It is twelve.
First of all to correct your English Grammar. The singular 'I' is always written as a CAPITAL letter, where ever it appears in the sentence. So your question should read ' How do I write 12 in word form ? '. To answer your question the number '12' is written as the word ' twelve'.
How
Twelve.
12 = twelve.
Twelve.
The number 12 in word form is 'twelve'.
Twelfth or 12th.
Twenty one and 12 hundredths
7 trillion 12 billion.
Sixteen and eleven thousandths.
Twelve and twenty five thousandths.
12 point thirty eight or 12 and 3 tenths and 8 hundredths