On the back of the radio, are there any connections for an external antenna? They come in many forms; sometimes they're screws that you tighten down on top of the wire. Sometimes there are thumb screws instead of plain screws (these are called "binding posts.") They could also be holes that you open by pressing down on a spring-held clip (the clips hold the wire in the hole after it is placed. This type of connection is also common on loudspeakers.) If there are, they should be labeled "300 Ω" and 75 Ω".
If the antenna is the type that is shaped like a tall "T" and is meant for indoor use, connect it to the 300 Ω terminals. Outdoor antennae connect to the 75 Ω terminal.
Please bear in mind that I'm far more familiar with older (i.e. made no later than 1980 or so) radios/receivers/tuners, but I doubt that they've changed too much.