The endings are standard -ir verb endings.
Yo-Prefiero
Tu-Prefieres
El/Ella/Usted-Prefiere
Nosotros(as)-Preferimos
Ellos/Ellas/Ustedes-Prefieren
The stem-change is e-ie with the second e (preferir to prefier-). This occurs in all conjugations of the verb but the nosotros(as) form. This is the same with all stem-changing verbs in the present tense.
Hope this helps!!
