Even in language and reality, something that has "and" with them means both of them are necessary. (This is ignored most of the times though)
For example, "You and Her are summoned to attend the meeting".
It means both of them are summoned to attend the meeting, not just one of them.
If only one of them, that condition will not return true.
same goes with the if statement. Both conditions must be fulfilled for it to return true.
It takes both of the conditions into consideration before starting the actions of the other tasks.