cmd - What does "&&" do in this batch file?

Question

I received a line of code from someone who answered one of my questions, but I am confused: what do the "&&" do in this batch file.

@echo off
set /p Quest="How are you today? "
echo %Quest% > Results.txt
findstr /r /i "not.*good not.*well" Results.txt >nul && echo Sorry && goto pause
findstr /i "good well" Results.txt >nul && echo My day is doing good as well
:pause
pause

Answer 1

&    separates commands on a line.

&&    executes this command only if previous command's errorlevel is 0.

||    (not used above) executes this command only if previous command's errorlevel is NOT 0

>    output to a file

>>    append output to a file

<    input from a file

|    output of one command into the input of another command

^    escapes any of the above, including itself, if needed to be passed to a program

"    parameters with spaces must be enclosed in quotes

+ used with copy to concatenate files. E.G. copy file1+file2 newfile

, used with copy to indicate missing parameters. This updates the files modified date. E.G. copy /b file1,,

%variablename% a inbuilt or user set environmental variable

!variablename! a user set environmental variable expanded at execution time, turned with SetLocal EnableDelayedExpansion command

%<number> (%1) the nth command line parameter passed to a batch file. %0 is the batchfile's name.

%* (%*) the entire command line.

%<a letter> or %%<a letter> (%A or %%A) the variable in a for loop. Single % sign at command prompt and double % sign in a batch file.