What do i need to connect my dell monitor to my iMac for dual monitors
The brand doesn't matter. Just plug it into whatever port works. You might need an appropriate adapter, such as an HDMI to VGA or a Thunderbolt to DVI; it depends on which Mini you have and what input ports are on your monitor.
When using an external display with an iMac, it's called video mirroring - take a look at this Apple article:
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