Learn Dutch: Ik kook.

The full dictionary verb is koken. To get the ik-form (the stem), you remove the -en ending. That leaves kok. However, the 'o' in koken is a long vowel. To keep that long vowel sound when the word ends in a consonant, Dutch spelling rules say we must double the vowel. That is why it becomes kook.

Can Ik kook also mean "I am cooking"?

Yes! Dutch does not have a separate "am doing" tense like English does. Ik kook translates to both "I cook" as a habit and "I am cooking" right at this moment.

Is kook the only form of the verb I need to know?

No. The form changes depending on who is doing the action. The bare stem kook is specifically the ik-form (for "I"). For other people, like hij (he) or zij (she), you generally add a -t to the stem to make kookt.