I just want to erase my iMac so I can sell

I just want to erase my iMac.Model Name: iMac Model Identifier: iMac19,2 Processor Name: Quad-Core Intel Core i3 Processor Speed: 3.6 GHz Number of Processors: 1 Total Number of Cores: 4 L2 Cache (per Core): 256 KB L3 Cache: 6 MB Memory: 8