Using variables in pathnames and pathname variable help plus finding username applescript?

So, I want to have my script to be able to find out the current user's username and store it in a variable (myUsername). Then, it will go to /Users/myUsername/Desktop/FV.app. How can I do this and insert the variable in the file address in order to open the file? Your help is very appreciated! If any clarification is needed, I will reply.