You smash the windows with (shotgun) or shovel.
You toss the molotov cocktails in the windows.
You kill vargos as you find them during the mission.
You enter the building.
You get the fireextinguisher from the kitchen.
You go upstairs.
You use the FX to put out the fire at Denise's door.
You meet D.
You led her out.
You use the FX to put out the fires that would otherwise preevent D from leaving.
You hug her.
You drive home.
IF CJ is Fireproof (from doing the Firefighting Missions) it is slightly easier, and very helpful for later missions.
If you have a PC you may use:
Samutz's Uploader/Downloader: http://www.gtasnp.com/
to upload your game save for someone here to do it for you.
Else, we can only tell you what needs to be done. This post has been edited by lil weasel on Sunday, Apr 22 2012, 16:38