You have to buy a amiga rgb2vga adaptor and then it will work with a very few monitors that supports the low refresh rate of a standard amiga. The other option is to buy a flicker fixer vga adaptor, which will not only convert the signal to vga but will also double the refresh rate, so that it is compitable with most vga monitors.
The only Amiga that comes with built in vga and flickerfixer is the a3000.
The Amiga1200 works fine with a normal tv though, but the quality will not be as great as with a monitor.