Metlieb's notes to go: Gotować = to cook in general, as in I like cooking/lubię gotować. Ugotować = too cook something, implying that you have the intent of finishing the process of cooking, as in I want to cook a soup / Chcę utogować zupe. The same is true for many other verbs taking the u- prefix: Uwolnić / to set free, ubrać / to put on (clothes), upiec / to bake. Also note that some verbs only exist with the u- prefix for some reason.
Well... they are completely different categories.
Modals are verbs that 'connect' with other verbs, like "I want to cook soup" or "I have to write this essay".
You can translate "to cook" as imperfective "gotować" or perfective "ugotować". Imperfective focuses on the process. In this sentence here, it would mean that you want to cook one thing for a period of time? It's not wrong, but rather weird.
"ugotować" as a perfective verb focuses on the result. And most likely you would want to cook something succesfully, til the end. As perfective verbs could be said to refer to the moment of finishing the action, they cannot be used in the Present Tense.