Add /usr/racket/bin to your PATH. If you use bash (which is the default for the terminal in Ubuntu), you would edit your .bashrc file to have the two lines:

PATH=/usr/racket/bin:$PATH

export PATH

If your .bashrc already has a PATH setting, then you need to add /usr/racket/bin to it. For example, I already have a PATH setting that looks like: PATH=~/bin:$PATH. I would then change it to: PATH=/usr/racket/bin:~/bin:$PATH. The colons act as separators while $PATH will include whatever your default environment PATH is. Bash will look in the locations in the order listed, so actually I would probably prefer PATH=~/bin:/usr/racket/bin:$PATH so that my personal scripts (which I put in ~/bin) would be picked over anything else.

If you don't have a .bashrc in your home directory, make one using your favorite text editor with the two lines above.

The modification won't take effect until you open a new terminal or you type source .bashrc in the current terminal.

Add drRacket to the "open with" submenu of the right-click menu. I think you are probably using the default file manager, Nautilus. I don't use that anymore but my understanding is that people have been having problems with this. See this answer for a solution.