In French, it would be "Suce mon pénis puant" ("Suck my stinky penis"). "Sucer" is the infinitive form, the base form of the verb, whereas "suce", in this sentence, is the second person singular imperative form. Here, it's an order.
In English translated into French, "suck" can mean many different things, depending on the person, the tense, the context. "To suck, I suck, you suck, we suck, you suck": the only thing telling them apart is the word that comes with it. "Suck" alone is the bare infinitive, "to suck" is the full infinitive.

In French, "suc-" is the root of the verb. Anything that comes after helps identify how it's conjugated. However, if the suffix begins with an "a" or an "o" ("u" is not used in this example), you need to change the "c" to a "ç", a c-cedilla to keep the "s" sound and not end up with a "k" sound.
In English, you sometimes forget all these diacritics in loanwords.

POOMP EET