Hi! You may have experienced an issue where you want to make a humanoid-less character / want to make a custom character rig, but cant get the shirts and pants to load on it. There is actually a relatively simple solution! In blender, you can change the unwrapping of the mesh to directly support shirts and pants!
The first step is to open the mesh you want in blender, and then go to edit mode.
Next, make a new window in blender.
https://gyazo.com/4b5d12851b4db8fb004abfe5918b586e
Then, click in the top left of the new window and select UV Editor.
https://gyazo.com/0134bec921ba0a55182991f5ea7c55c2
Then get the roblox shirt template image (I recommend using the r15 template)
After that, press image in the new window, then click on open.
https://gyazo.com/f160d3b45845d204383d1ee9361c7dba
Then select your image.
Go back to the right sidebar, and press the materials tab.
After that, press the plus button and click on the dot next to BaseColor
Then click on image, and select your template image.
Then change it to Shading mode
Next, Shift+click the vertices you want the front of the shirt/pant limb to be on.
In the menu on the right, you should see 4 dots appear. Move these until they match up with the clothing front.
Repeat the last 2 steps until you have the limb fully mapped!