Mixed tenses (I go, I am going, I went, I was going, I have been)

We use the present simple to describe permanent states, facts and regular activities, e.g. where we live and what a company produces, e.g.
I work in Bielefeld.
He / She / It works ….
We / You / They work …

The present continuous is used to describe temporary actions or events which are either happening at the time of speaking (I’m writing an email at the moment) or events of a longer term but still temporary nature, which are happening around now, e.g.
I am working on a sales project this week.
He / She / it is working …
We / You / They are working …

The past simple is used to describe fully completed events in the past. We often use a time indicator (e.g. yesterday, last year, in 2003 etc) but we don’t always have to mention it – important is that the context must be about this past time, e.g.
I worked in Bremen yesterday.
He / She / It / We / You / They worked ….

1. To describe an action of duration in the past covering a specific time, e.g.
I was working at 11am yesterday.
2. To describe an event of duration in the past (past continuous) interrupted by another event (past simple), e.g.
He was writing an email when the phone rang.
3. To describe two parallel events of duration in the past, e.g.
We were speaking to a customer while John was giving a presentation.

We use the present perfect to talk about:
1. A current situation that started in the past
It connects a time in the present with the past. This is often in connection with the words “for” and “since” (if you think about the words, they always create a link to the past), e.g.
I have worked here for four years (I still work here!)
2. Past experiences where a time is not specified , e.g.
He has been to Berlin (no time given).