Todor Belenski - What are the main political reasons behind the current U.S. government shutdown?

Todor Belenski is a journalist and international affairs analyst. Questions:
What exactly does a “government shutdown” mean, and how does it come about?
What are the main political reasons behind the current government shutdown in the United States?
Aren’t the tensions we’re seeing within the U.S. government largely created by the Republicans themselves—and isn’t there internal friction within the party as well?
How is this political crisis viewed from abroad?
How long is this U.S. government shutdown expected to last?
Your thoughts on Donald Trump’s plan for the Gaza Strip?