English Grammar - Perfect And Perfect Progressive Tenses

I'm still studying.

I studied until a little while ago.

He's still doing his homework.

He's finished his homework.

First he was watching TV. Then his friend arrived.

First his friend arrived. Then he watched TV.

First he was watching TV. Then his friend arrived.

First his friend arrived. Then he watched TV.

I'll start level 5 before next quarter begins.

I'll start level 5 when next quarter begins.

I'll start level 5 before October.

I'll start level 5 in October.

The house was already clean when I arrived home.

The house was not yet clean when I arrived home.