Short answer: If you want to play games, you need a
ScanDoubler, which will convert all Amiga screenmodes to VGA frequencies, and display them on any VGA monitor. An alternative would be one of
these screens, or something similar.
If you don't want to play games and only want to use Workbench and OS friendly appplications that open on Intuition (?) screens, then you can just use an adapter cable to connect the monitor to the Amiga's output, and set the application to use a resolution at VGA frequencies.
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moto