Answer:
Yo estoy delante de la puerta.
Explanation:
The word "delante" means "in front of," so it is not a word that needs to be conjugated. Since you are talking about the location of an object (yourself), which can be changed over time, you use the verb "estar." Estar is an irregular verb in first-person singular, so conjugating it in the present tense is:
yo estoy
tu estás
el/ella/usted está
nosotros estamos
vosotros estáis
ellos/ellas/ustedes están
Hope this helps!