possum

Possum is not really a new verb to learn. It is sum with pot-, able, stuck on the front, and reading it that way makes the present fall straight out: possum, potes, potest, possumus, potestis, possunt. The only wrinkle is a sound rule. Where the form of sum begins with s, the t of pot- assimilates to it and you get possum, possumus, possunt; everywhere else the t simply stays, potes, potest, potestis. The infinitive is posse, the perfect potui, and the verb it governs stands in the plain infinitive with no ut in sight.