Answer:
When conjugating verbs that end in -er and -ir, there are similarities and rules to follow as long as they are regular verbs.
For example let's conjugate and compare two verbs, "comer" (to eat) and "escribir" (to write) in their simple present form
Yo como Yo escribo
Tú comes Tú escribes
Él come Él escribe
Nosotros comemos Nosotros escribimos
Ustedes comen Ustedes escriben
Ellos comen Ellos escriben
In the examples the bold part represents the terminations following the root of the verb. As you can see, the terminations are the same except for the first person plural, which is where they differ.
