One is a verb, to cook = kochen (note the lower case "k"). Also, "sie kochen" = they cook and "Sie kochen" for the polite form of you cook.
der Koch = the cook (noun, male).
die Köche = the cooks (noun, male plural).
die Köchin = the cook (noun, female).
die Köchinnen = the cooks (noun, female plural).
The umlauts matter. On the PC version, they are given below the typing field. On a mobile phone, hold the "o" key down a touch longer to find ö. If that doesn't work, spell ö as "oe".
Fingers crossed I got all that right !!!