Je vais travailler demain.

This verb is irregular — it isn't built from anything and has to be learned. Its full table is below, in the rule's explanation.

Mood

indicative

Tense

present

Person

first person singular (je)

With

Je

Irregular. There is no stem-plus-ending pattern to follow; the whole table has to be learned, like English be: am, is, are.

This verb is irregular — it isn't built from anything and has to be learned. Its full table is below, in the rule's explanation.

Mood

infinitive

This is the second verb, so it stays in the infinitive. When two verbs follow each other only the first is conjugated, like English I want to leave.