IF condition
THEN
stuff;
ELSIF condition2
THEN
otherstuff;
ELSE
stuff if not any of above conditions is met;
END_IF;
Above is elsif structure. Below will be what u wrote, that is two nested if's.
Code:
IF condition
THEN
stuff;
ELSE
IF condition2
THEN
otherstuff;
ELSE
stuff if not any of above conditions is met;
END_IF;
END_IF;
In this case it works the same, but its matter of "good code". Also in good programming practice is indentation to show "level" of instructions as shown above. It results in better readability of code.