In general, If WordPress function start with get_ such as get_the_content() or get_the_ID(), it will return results and it’s not going to echo anything. It’s useful when you have to manipulate the result before outputting or printing on the screen.
If WordPress function start with the_ such as the_content()and the_ID(), WordPress will echo the returned value and output will be displayed automatically on the screen.
When functions are used for internal logic get_ function is used and when the result is needed to be displayed on the screen the_ function is used.
What’s the difference between WordPress function get_the_content() and the_content()?
get_the_content() returns the requested post content. While the_content() echo the post content after applying the_content filter.
As get_the_content() does not pass the content through the the_content filter, the result of get_the_content() will not auto-embed videos or expand shortcodes and more.
This means the_content() is the output of get_the_contnet() that will be passed through the_content filter and echo at last.
Reference: https://stackoverflow.com/a/50893390/9877289
Also, visit WordPress Codex and WordPress Developer page to find exact detail of any WordPress function.