TRIS controls whether the pin is an INPUT or an OUTPUT.

PORT (when used as an OUTPUT) will control if the pin is LOW (0v) or HIGH (+5v).

Each PIC pin can actually have THREE STATES... (consider TRIS=TRIState) it can be... (for example taking PORTB.0)...

High Impedance (set for INPUT) when TRISB.0=1 (irrespective if PORTB.0 is set to 1 or 0)

OUTPUT LOW (set at 0v) when TRISB.0=0:PORTB.0=0

OUTPUT HIGH (set at +5v) when TRISB.0=0:PORTB.0=1

So, in summary, TRIS will set the pin (or Port) for INPUT or OUTPUT, but PORT will set the pin HIGH or LOW (once it is an OUTPUT).

Just to throw another variable into the equation, PORT can also be used for INPUT operations (when TRIS had previously set the pins/Port INPUT) thus...

MyVar=PORTB.0 ' Read the state of just PORTB Bit 0 into variable MyVar

MyVar=PORTB ' Read the state of ALL the pins of PORTB into variable MyVar