Hi my name is daniela.I have been in the us for 6 years illegaly.I want to get legal now.I have a fiancée and we want to get married.how do I start by becoming legal.

Not enough information. How did you enter the US? visa waiver, B visa, EWI?

If you initially entered the US on visa waiver or a visa, then after you marry, your USC spouse can file for your permanent residence. The filing under section 245(a) will forgive the visa/I-94 overstay and unauthorized employment.

Consult with an experienced immigration attorney to determine if you are otherwise eligible, as there are other grounds for denial such as previous immigration violations, criminal activity, etc.

Congratulations and good luck.