Well, considering you’re first starting off, I suggest you get AlreadyPro’s plugin to insert already existing ROBLOX characters into studio.
NOTE my tutorial here is for beginners, and in no way will be as high quality as you see on the front page. It is a start, and a way to expand your learning.
When I first started out, I would place the characters into studio and make sure they don’t give off shadows, and create a green screen with blocks.
If you want to make your character pose, I usually click play, go into my own character, and grab the second idle animation that I have equipped. For this we will use zombie.
Open up your animation editor on the rig that you imported, and put in the idle2 id, and put the slider to where you think looks the best for what you’re making. (usually opening the editor, selecting and anchoring your character, file - import - ctrl v animation ID, then slide.)
When you are done, duplicate the character and click out of the animation editor, and delete the rig that is not animated.
You can use a screenshot software such as Lightshot to capture your character, and with Paint.net crop out the greenscreen in the back.
Now, if you really want to be high quality, I suggest you get a rendering software such as Blender but it is extremely in depth and you would need to learn how to use the software.
Hope you found this helpful