Learn French: Je corrige les erreurs sur l'écran. - I correct the mistakes on the screen.

No, corriger (to correct) is mostly a regular -er verb, unlike the irregular verbs in this lesson. The only special rule is that in the nous form, we add an e (nous corrigeons) to keep the soft g sound. The je form here is completely regular.

Is erreur masculine or feminine?

It is feminine (une erreur). It can be tricky to tell when looking at the plural les erreurs, but many abstract nouns ending in -eur are feminine in French. Other common examples are la couleur (color) and la peur (fear).

Why do we use l' in sur l'écran?

We use l' because écran (screen) starts with a vowel. In French, the singular words for the (le and la) drop their vowel and become l' before another vowel or a silent h. This makes pronunciation much smoother!

Is there another word for mistakes that I could use here?