Starting Grammar

I have started to dip my feet into Chinese grammar. This link is has been very useful for getting me started on the tenses. In one of my previous posts I used the past particle (了) incorrectly. According to the link above the past particle is never used on the verb to be (是). I was supposed to use a time specification (last week, yesterday etc.) after the subject. As I haven't covered time and time frames anywhere I will leave the fixing up of my previous grammatical error till later.