Topic:   GRAMMAR:  THE PRESENT TENSE

All regular verbs which end with -ar behave in the same way that CANTAR does:

CANTAR                    TO SING
Canto                         I sing
Cantas                       You sing
Canta                         S/He sings
Cantamos                  We sing
Cantáis                      You sing
Cantan                       They sing               


All regular verbs which end with -er behave in the same way that COMER does:

COMER                    TO EAT
Como                          I eat
Comes                        You eat
Come                          S/He eats
Comemos                    We eat
Coméis                        You eat
Comen                        They eat             

Unfortunately , verbs which end in -ir are mostly irregular.  There are rules but they apply rarely.  If you need an -ir verb, make sure it's a common one which you have learnt by heart.  If you have not, don't use it!