When you conjugate ar, ir and er verbs you remove the infinitive ending and then you add the ending that matches the subject. I think you're trying to ask how you can differentiate between ar, ir and er verbs after they are conjugated so I'll type a little example:
hablar
yo: hablo
tú: hablas
ella, el, usted: habla
nosotros: hablamos
ellos, ellas, ustedes: hablan
comer
yo: como
tú: comes
ella, el, usted: come
nosotros: comemos
ellos, ellas, ustedes: comen
vivir
yo: vivo
tú: vives
ella, el, usted: vive
nosotros: vivimos
ellos, ellas, ustedes: viven
I don't know how to explain this properly but, when you compare the three you can see the obvious differences. Like you stated, they are similar but they are also very different. (Hope this helps? Language is a very hard thing to understand immediately. Good luck!)