To make a torso, use part number 3814. The part number you were searching for is the decoration specific id that will bring up the suit jacket torso. Here's a link that will walk you through the process. I don't have a minifig specific part on the tutorial, but it's coming soon.

Here's a link for my custom decorations tutorial:
How to Make a Custom Decoration

Here's the minifig section:
Let's Build a Minifigure!

Thanks, it worked!

Wonderful!

What number do I use for legs?

Thank you. When I try to use 73200 nothing will come up.

What are you trying to do? Are you in the workshop or the part manager?

Sorry I figured it out.

I have a question. Is there a way to add something to a official piece? Like a logo?

The most reliable way is to export the model, extract the image file, modify it and then re-upload it. Try using the colada .dae option.

i have a question. when i try to use the part number 19303 (the ultron helmet) nothing comes up.

So, that part has not been updated yet. You can tell this because when you search for it in the library, the icon does not have the "2" in the upper corner. Here's a link that explains it:

Step 1: Can I decorate this brick?

I can't seem to add custom decoration to a torso?

There's a 2 in the corner...

You need to create a custom version of just the torso (3184) first before you create the full upper part.

@Snaz-

XForce nailed it. Here's a full step-by-step for minifigs:

Let's Build a Minifigure!

Got it. Thanks!

i want to custom helmets

which ones?

can you do custom heads?

You sure can...

Let's Build a Minifigure!