:salam2:
welcome to tti. now the first thing you have to do is say the shahada.
actually first you have to believe in your heart that Allah is the only true God worthy of worship and muhammad ibn abdullah is the slave and final messenger of Allah.
You have to believe in all the prophets named in the quraan.
you must also believe that psalms, Torah and gospel in their original forms were from Allah and Quran is the last and final revealed text. it's the verbatim word of Allah.
you must believe that there are angels who carry out Allah's orders and jinns who are like humans, creation of Allah.
since you were a catholic you must believe that Jesus/Isa (as) was a slave and messenger of Allah. he is not divine nor is he and incarnation of God. He is not dead and wasnt crucified. he will come back before the end of times.
last but by know means the least you must believe that
everything (good or bad) happens by the will of Allah. Nobody can surpass His will.
If you believe in all that than say your testimony of faith right now!
“ASH-HADU ANLA ELAHA ILLA-ALLAH WA ASH-HADU ANNA MOHAMMADAN RASUL-ALLAH”.
he English translation is :
“I bear witness that there is no deity (none truly to be worshipped) but, Allah, and I bear witness that Mohammad is the messenger of Allah.”
http://www.islamqa.com/en/ref/11819