I have an '03 Civic LX 4-dr and I'm confused about strut bars. Do I need 2? 4? Front upper and lower, rear upper and lower? Tie bars? What's up. Thanks people.

 

there are 2 upper strutbars, front upper and rear upper. there are 2 lower tie bars, front lower, rear lower.

 

You can use them separately if you want. There are also lower H-braces.

 

Strut bars prevent your strut towers from moving when turning. If you are doing some kind of racing that involves turning, they are something to invest in.
Anti-swaybars link the ends of the lower control arms.
Tie bars, I don't know what they do.