Yes it is fine to listen, you do not want to try to transmit with out an antenna and proper tuning or you might damage the output section of the radio.
First question:
If it was still in the box, rummage around and see if the paper work is in there, a user`s manual. If it is, grab a cup of coffee and sit down and spend some time and read it. That will outline the functions of the radio, and how to use it. The Ft 102 is a very nice radio, and if you found it as a freebie and it is working you just scored a real nice radio.
That would be my first step, dig around on the net and see if you can find a user`s manual
That radio cost upwards of $1000.00 new depending on what filters and options it has in it.
( by the way, it is spelled " Yaesu" And they ARE the choice of the worlds top DX`ers)
Do a search On line, there is a User group on yahoo devoted to this radio.
You will need an antenna and also need to learn how to set the radio up to listen on the band that you want to listen to. It is not a real good starter radio due to the fact that is can be a bit complicated, but I can not stress enough how much of a sweet radio it is.
Let us know if you find the book in the box, and we can go from there.
73
Jeff