じょせい(女性) is a formal expression. 女の人 is a little bit less formal. These two words have the same meaning.

You got me curious, so after a bit of research, it seems じょせい can be used for inanimate objects. So in America it's common to assign a gender to your car (I know, it's weird) If I know what I'm talking about "わたしのくるまはじょせいです。” would be 100% grammatically correct.

if I had to guess, じょせい is probably less formal. There's also 女生 (Schoolgirl) so try not to get those mixed up.