The part is never created because you never gave it a Parent.
When you use Instance.new() you should always assign a Parent to the Instance. It's usually best to leave this for last and allow the other properties of the Instance to come first. If you fail to give the Instance a parent it will float around in thin air.
Also, when you are using the constructor, Instance.new() returns the created Instance, and thus you'd have to assign it to a variable. Without assigning it to a variable the compiler will have no idea what you're referring to.
Going to this: "because you have 2 Parts in workspace". The second part was never given a parent. If your initial idea was to edit the newly created part, then parent that new part to the Workspace and give it a different Name so it doesn't get confused with other Instances called Part.
3 comments
Now it says that Part is not valid member of workspace
Can you show me the script?
Put the part in the workspace