I trying to get to grips with ubuntu(as a brand new convert). The only commands I am entering into the terminal are things like 'sudo apt-get update' or 'sudo apt-get install build-essential bison flex libsndfile1-dev libasound2-dev libqt4-dev libqscintilla2-dev'.

The installs and updates haven't quite been working as I want(I don't know the causes yet), I just want to know if I can experiment, exit terminal and reinstall things that I have already tried to install without causing problems to the system. 

For now I just want to have peace of mind in my trouble shooting, before I need to ask more specific questions about issues.

Much appreciated!