Does your gym have any group fitness classes? That is how I got started. I took one they called "Pump + Abs" which I guess is similar to something called body pump or other similar names out there. It appears it had similarities to P90X, too. The classes were pretty challenging for me and the exercises had various modifications I could do as a rank beginner. So while other people were doing planks on their feet and elbows I could do them on knees and hands. Stuff like that. It really was a good start for me. I've moved on to doing weight lifting with barbells. I hired a personal trainer for 3 sessions to show me how to use the equipment and help me choose appropriate starting weights. (The personal trainer was associated with the university where the gym is, but it's not like she's an employee of the gym.) After I got instruction from her, I followed the illustrations in Starting Strength (a book I bought online) to make sure I continued to use proper form and also for the general idea for linear progression. I even bought some giant washers so I could put smaller increments of weight on the bar.
So I've gone from not being able to do a plank and feeling like my internal organs were pressing right on the floor if I laid on my belly to being able to do a real plank for 2 minutes (or more, never tried to see how long I could do it.) I can squat 95lbs for reps, deadlift 115lbs for reps, bench 60lbs for reps, overhead press 50lbs for reps. No pullups yet.
Female, 5'3", 49, Starting weight: 163lbs. Current weight: 135 (more or less).
Starting squat: 45lbs. Highest squat: 167.5 x 2. Current Deadlift: 190 x 3