An antenna picks up aerial waves. A tuner will extract waves in one narrow range of frequencies from the antenna and do something with it, like outputting it to a component in a VCR or older TV set.
I have been successful at using antennae for short-range (802.11 range) broadcasting as well, though, when I output a RF signal from a RF amplifier. An antenna is thus a passive device, where a tuner is an active one.
Due to the advent of fractal antennae, it may be possible to cram one inside a TV. after all, this is how cell phones pick up signals today without giant extendible antennae. Though if you live in the united states, analog TV is dead, so you may need to get a converter for digital television, if your TV wasn't made after something like february 9th, 2009.