Do I have to share the source code of my Qt Application?
If you release your application as LGPL, then I think the license says you must make your source code available. Do not use a license if you do not understand it and consult someone who can explain all of the terms to you.

You can use LGPL components (like Qt) in your application without releasing your application with the same license. You can make a commercial application and sell it even though it uses LGPL libraries. However, you do have to provide either the source code to the libraries or a link to a site where users can obtain the source code for them.

You cannot use GPL components in a commercial project or in a project where you do not release its source code.