Ir and -er ending verbs are very similar in their endings when they are conjugated how do they differ in their endings when they are conjugated?

Historical introduction: understanding its conjugation

The future was originally form by adding the forms of "haber" to an infinitive (remember that the h is not pronounced in Spanish):

comer he (eat I must) → comeré

comer has (eat you must) → comerás

comer ha (eat he/she must) → comerá

comer hemos (eat we must) → comeremos

comer habéis (eat you must) → comeréis

comer hán (eat they must) → comerán

In other words, the endings are identical to the present indicative of "haber". Possibly for this reason, it is by one of the most regular tenses in Spanish: there are about 12 verbs with irregular futures, plus other verbs that were created by adding a prefix to them, like decir and predecir, or poner and componer. These prefixed verbs always follow the same pattern.

This "eat you must" is still reflected in commands, like the ones in the Bible:

No matarás = you shall not kill

No irás a ninguna parte = You are not going anywhere

There is a difference usually in the conjugations in first person plural.

Explanation:

When speaking of regular verbs, based on their infinitive termination there are rules to conjugate. Lets do an example with the verbs "comer" and "escribir", both regular verbs with the -ir, -er terminations. I will conjugate below and write the standard terminations in bold.

yo como

tú comes

él come

nosotros comemos

ustedes comen

ellos comen

yo escribo

tú escribes

él escribe

nosotros escribimos

ustedes escriben

ellos escriben.

As you can see, there is a difference in the first person plural terminations.