First, one should know not to tinker with the default installation of LTspice. That is, custom libraries, symbols and such should reside elsewhere, preferably in the same folder as the project in use. Having said these, after placing the Filter in the schematic, it will look like this:

the symbol of the Filter

The pins, as noted in the image, are:
Only pins IN, OUT and GROUND are mandatory for simulation and their meanings will not be repeated further in the descriptions. Pins 0.1, 0.2 and 0.3 are optional, while pin 0.4 depends on the filter. Unused ones can be safely ignored, no matter the case. With the exception of Analog Passive filters, the input is floating, i.e. there is a G-source as a buffer, and the output impedance is a current source with a resistance, therefore the input must be connected if the symbol is placed in the schematic, but not used.

©Vlad, 2008 - 2015