Hi Samira,
Many things to do in Lisbon:
- To Visit: Castle (stop in the nice coffe Chapito to chill out - one of the best views of the city), the typical Neighborhoods of Alfama and Chiado. All the Belem area with the great monuments (stop in Pasteis the Belem to do some touristic cliche thing and buy a Pastel = famous cake). If you have time don't miss Sintra (really amazing village half an hour from lisbon).
- Nightlife - Don't miss Bairro Alto (famous neighborhood), unique spot to go out, relax, hang around the narrow streets - (usually people stand outside the bars on the street), have some drinks, meet many people (nightlife in Portugal doesn't start before midnight - but you can go to Bairro Alto around 21h, 21:30 to have dinner first), if you like discos don't miss Lux.
Shopping - Chiado (downtown) or one of the many shopping centers.
How much time will you stay here?
Regards
Filipe