Present perfect and past simple

Present perfect.
The present perfect has the following uses:

°Recent events.
Examples:
-Sales figures have improved recently
-We haven´t seen a big rise in demand.
- Has your manager just started?


°Events that affect the present situation (but we don´t say when they happened).
Example:
-Prices have gone up so they´re very high now.


°Unfinished events starting in the past and continuing up to the present (using for and since).
Examples:
-I´ve been in sales since 1992.
-The company has beeen the market leader for three years now.


°Answering How long? about an unfinished event.
Example:
-How long have you worked for Exxon?


Key words:
recently, in recent months / years, in the last month / year, just, now, since, for (except with finished periods of time).




Past simple.
The past simple has the following uses:

°Events that happened at a definite time in the past.
Examples:
-I joined the company in 2003.
-The new secretary didn´t come in yesterday.


°Finished actions or events.
Examples:
-When you were a student, did you work in the holidays?
-Yes, I worked for a telecoms company in the holidays.


°Finished time periods (with for).
Example:
-Aisha worked in the finance department for two years, from 2003 till 2005.


Key words:
in 2005, from 2002 to 2004, las week / month / year, yesterday, ago, in the past.